The participants included 7,055 individuals in 1994 and 7,957 individuals in 1997. They all worked 35 hours or more per week at the time of the interview. They represented more than 78.7 million full-time workers in 1994 and more than 81.8 million in 1997. Although the rate of drug use is higher among unemployed persons than among employed persons, 70 percent of all current illicit drug users ages 18-49 were employed full-time. About 7.7 percent of the full-time workers ages 18-49 in 1997 reported illicit drug use in the past month; 7.6 percent reported heavy alcohol use (5 or more drinks per occasion on 5 or more days in the past month). The full-time workers in this age group included 6.3 million current illicit drug users and 6.2 million heavy alcohol users. These numbers included 1.6 million people who used both an illicit drug and were heavy alcohol users. In 1997, 44 percent of current illicit drug users worked in establishments with 1-24 employees, 43 percent worked in establishments with 25-499 employees, and 13 percent worked in large establishments. Workers who reported current illicit drug use were more likely than others to have worked for three or more employers, to voluntarily have left an employer in the past year, and to have skipped one or more days of work in the past month. Tables; figures; appended questionnaire, methodological information, and tables; and 15 references