Despite airtight double doors, disposable laboratory clothing, frequent decontamination and other precautions, accidental infections can happen at U.S. biological laboratories. Perhaps worse, though, is that accidents are going unreported. Although the U.S. has not confirmed any cases of sick scientists spreading their lab-derived infections to the public in the past 40 years, the case of the tuberculosis-carrying traveler Andrew Speaker shows that modern jet transportation could quickly spread deadly infections globally. Most important, the culture of nonreporting and lax enforcement of already weak incident-reporting regulations in the U.S. could make such secondary infections more likely. Indeed, some scientists believe they may have already occurred, as they have in other nations in which lab infections of smallpox, SARS, Marburg and H1N1 influenza viruses have spread to the general public.