A national survey of working adults conducted in 1985 revealed that a substantial proportion of working adults use illicit drugs. In addition, the most significant indicator of drug use is age; drug use rates also differ greatly according to sex, education, and job category. Marijuana and cocaine use were much more prevalent among employees under age 35 than among older employees and more prevalent among men than women. Current marijuana use was reported more often by employees who did not complete high school than by employees with more education and among skilled trade workers, sales personnel, business owners, and service workers than among other occupational groups. These results are similar to those from subgroup analyses of the NIDA Household Survey data. The main methods for estimating workplace drug use are self reports and drug testing. These two methods have complementary strengths and together probably represent the best method of obtaining prevalence estimates at the level of the individual company or industry. A household survey of the working population would be the most appropriate method for obtaining national data on drug use prevalence in the workforce. Tables and 15 references