As the dizziness began to fade and nausea to subside, I kept thinking how two tablespoons did not sound like a lot of blood. During regular checkups, my physician draws only about half that amount. I suppose I might have guessed, especially after a 12-hour fast, I would sicken when my glucose levels dipped--I'm a terrible blood donor in that regard.

The nurse who drew my blood helpfully looked around my office for a sweet drink. "Do you have any soda or juice?" she asked. But the only thing I had was a can of Diet Coke. Which in a way is ironic: I used to drink regular Coke but switched to the sugar-free form after blood tests revealed that my triglycerides were too high.

Momentary ill feelings, though, were an acceptable physical price for 250 blood tests done at once--I was told that running them separately with conventional means would require a liter of blood. Imagine how dizzy and nauseated I'd feel then. So how could I not roll up my sleeve for Biophysical Corporation? The Austin, Tex.-based company promised to use the blood to screen for presymptomatic cancers, potential immune disorders, latent infections, undetected hormonal imbalances and unrecognized nutritional deficiencies. It seemed to mark a step toward that Star Trek future in which Dr. McCoy waves around a saltshaker device to determine a person's medical secrets. ("Heartbeat is all wrong. Body temperature is ... Jim, this man is a Klingon!")

The Biophysical250 assessment, as the firm calls it, is more than just a battery of tests. It includes a medical-history interview; a personal visit to the home or office for the blood draw (I should have picked my home, where I actually keep sugar); and a follow-up physician consultation. All this attention does not come cheap. It costs $3,400, and it is not covered by health insurance. The company states that doing each test individually would cost 10 times more, so Biophysical250 is a bargain by comparison. Still, you need some disposable income, or you must be so indispensable to your employers that they will pay for it. I don't fall into either category. But because I was reviewing its product, Biophysical agreed to conduct the test on me for free.

The analysis focuses on blood biomarkers, which are chemicals whose presence or amount may indicate abnormal processes or reactions in the body. Among the most familiar are cardiovascular ones: high- and low-density lipoproteins (HDL and LDL, the good and bad cholesterols) and triglycerides.

Checking 250 biomarkers at once might seem like overkill. A routine exam screens for two or three dozen. Looking at one biomarker in isolation, however, is usually not especially informative--for instance, the ratio of LDL to HDL is more important than either alone. The Biophysical250 takes it much further: to assess the risk for heart disease and stroke, the firm analyzes 33 biomarkers.

And examining several biomarkers together improves the odds of finding problems early, especially malignancies. Blood tests for cancers have been problematic, because healthy people may produce the same kinds and amounts of the biomarkers that cancer patients do. Moreover, the chemicals do not always show up in cancer patients, and they may result from unrelated conditions. The Biophysical250 screens for about four dozen blood chemicals tied to cancerous activity in general to increase the odds of detecting presymptomatic disease.

As an example, Biophysical points to ovarian cancer, which is usually diagnosed too late. Cancer antigen 125, the most commonly measured marker for the disease, shows up in only half of patients in stage 1, when treatment is most likely to succeed. The Biophysical250 tries to boost the chance of early detection by measuring other, biologically independent compounds, such as vascular endothelial growth factor, interleukin-6, and monocyte chemoattractant protein. "Just the fact that we stack so many biomarkers really minimizes false positives," comments Mark Chandler, CEO and founder of Biophysical.

The firm has basically miniaturized the standard blood tests, substituting the microliter wells with tinier polystyrene beads, each about half the size of a red blood cell. Each sphere is coated with a particular antibody. The serum from the blood sample mixes with the beads for 15 to 30 minutes, allowing the antibodies to grab onto the proteins they recognize. After the serum is washed away, another of the same set of antibodies goes in. This time, though, each antibody also has a fluorescent tag. The tagged antibodies sandwich the blood proteins already held by the first set of antibodies. Examining the fluorescent tags thus provides "an idea of how much of the chemical was pulled out of serum," explains Chandler, who began selling the Biophysical250 -assessment last year.

My report arrived two weeks later via FedEx. It included a well-written summary plus a quantitative laboratory report. A second booklet defined all the biomarkers and the ailments with which they correlated. In terms of health, the most useful part is the summary of biomarkers organized by type: autoimmune, cancer, cardiovascular, cell signaling, diabetes, endocrine, hematology, immune/inflammation, infectious disease, nutritional, organ systems and osteo-arthritic. Next to each biomarker was a color code, depending on whether the detected amount was out of range: green for "low risk," yellow for "caution" and red for "alert." The report also came with a copy to give to my personal physician; Biophysical will discuss the results with a client's doctor. I also later had a telephone consultation about my results with George Rodgers, the company's president and cardiovascular specialist.

My results were mind-numbingly normal. Most everything came up green. The only surprise was my slightly out-of-range ferritin, a protein that stores iron. My report warned me that such iron overload might signal a genetic condition called hemochromatosis. The disease progresses silently and can cause toxic levels of iron to build up in organs. The treatment is simple--regular blood donations to drain off the excess iron. On the other hand, my ferritin level might reflect the fact that I had been taking a multivitamin with iron--a no-no for healthy men, I later discovered. It's something I'll check with my physician.

And therein lies a great strength of Biophysical250: it can uncover a pre-symptomatic, potentially fatal disease that physicians might not ordinarily test for. The firm reports that in an unpublished study of 120 clients, 15 turned out to have major health risks and another 27 indicated moderate risks; none showed outward signs of disease. The conditions included rheumatoid arthritis, scleroderma and hypothyroidism.

The company screens only for treatable ailments and avoids those that are invariably fatal. So for now, neurodegenerative conditions such as Alzheimer's disease are out. But, Chandler adds, the firm would consider testing for such illnesses "if there's a way to slow down progression of the disease."

My Biophysical250 results were limited in the sense that they reflect my health on January 10, 2006, at 9:30 A.M., when my blood was drawn. Biochemical changes over time, though, reveal more about the state of a person's health. But at the cost of a giant flat-screen plasma TV, the Biophysical250 is not exactly affordable, even if done every other year. Couldn't the company knock off a few of the tests? I mean, did I really need to find out that I have no African sleeping sickness parasites, considering that I've never been to Africa? Or to know that I am not pregnant?

Chandler says that plucking out a few of the beads would not be cost-effective, although perhaps a few dozen biomarkers might be enough to catch the most common afflictions and permit a less expensive assessment. He would like data from 10,000 clients before pruning the number of biomarkers. (He expects about 1,500 customers this year.) The company may head in the other direction and institute a Biophysical300 as research uncovers more biomarkers. I'd certainly be game for it if the price came down--and as long as it does not need more than two tablespoons of blood.