The current standard for occupational exposure to asbestos is 2 fibers/cm3 averaged over an 8-hr day. A NIOSH/OSHA committee has recently concluded that the 2 fiber/cm3 standard is grossly inadequate to protect workers from asbestos-related disease, and that all levels of asbestos exposure studied thus far have demonstrated asbestos-related disease. The committee recommends that a 0.1 fiber/cm3 limit replace the current 2 fiber/cm3 standard on the grounds that this is the lowest level detectable with currently available analytical techniques. Thus a 0.1 fiber/cm3 limit is not based on epidemiological data but on the presumption that any level of exposure is disease producing. This paper addresses the question of whether it would be possible to detect health effects of exposure below the current 2 fiber/cm3 standard. Five studies are reviewed which provide evidence on the strength of the relationship between asbestos fiber exposure and lung cancer. Calculation of sample sizes needed to be 95% certain of detecting the kind of excess probably associated with exposure to 2 fibers/cm3 suggests that epidemiology is not likely to be useful in detecting lung cancer below the current standard. Some outcome measures other than lung cancer or clinical asbestosis will be needed if observations on humans are to be used as evidence for a lowering of the present standard.