Advanced Cell Technology, for its part, has initiated dozens of clone pregnancies in cows and some in pigs. The company says it anticipates the first births in the near future. For these clones, the donor cells were fibroblasts taken from fetuses. The genomes of these cells can be relatively easily and precisely manipulated through a technique known as targeted gene replacement. "Advanced Cell Technology has the ability to produce transgenic animals using fetal fibroblast nuclear transfer," claims Steve Parkinson, president and chief executive officer.

Parkinson contends that targeted gene replacement produces cells having specific genetic alterations far more effectively than the traditional technique for making transgenic animals, which entails injecting DNA into cell nuclei. He reports that Advanced Cell Technology plans to clone genetically altered animals whose neural tissue would be immunologically compatible with that of humans. Clinical trials of such tissue on patients with Parkinson's disease could start by 1999, he says.

Cloning progress is not restricted to the U.S. Since the February breakthrough, PPL Therapeutics of Edinburgh, which collaborates with the Roslin Institute, has produced five lambs from fetal cells that were genetically modified to carry marker genes and genes for human proteins. Lambs produced from the genetically manipulated cells produce foreign proteins; such animals may be able to manufacture large quantities of medically valuable human proteins in their milk. The result "brings nearer the human benefits from nuclear transfer work," says Ron James, managing director of PPL. The same company is also working on cloned cattle in the U.S.

Dolly, then, was more than just an overnight sensation. Rather, cloning seems set to become a vital technology for agriculture and medicine. "I think the possibility is there that it might really move large-animal transgenic work forward much more rapidly," says Vernon Pursell of the U.S. Department of Agriculture. In other words, better forget the jokes and starting looking at the stock prices.