Data are presented on the use of these substances by the target population as a whole and by the following age groups: 12-17, 18-25, 26-34, and 35 and older. The report also examines trends in the prevalence of the use of the substances for the target population between 1972 and 1991. In addition, it analyzes the demographic correlates of the use of each type of substance among members of the target population. Further, information addresses patterns of use, problems that result from use, and perceptions of the harmfulness of using each of these substances. An overview is provided of the prevalence of the use of each substance among members of the population in six large Metropolitan Statistical Areas. In 1991, 37 percent of the target population reported having ever used an illicit drug; 12.7 percent reported having used an illicit drug in the past year; and 6.3 percent reported having used an illicit drug in the past month. The most commonly used illicit drug was marijuana, with 33.2 percent of the target population reporting use in their lifetime, 9.5 percent in the past year, and 4.8 percent in the past month. Other illicit drugs were used by fewer than 5 percent of the target population in the past year and by fewer than 2 percent in the past month. Of the target population, 84.6 percent reported having ever used alcohol; 72.7 percent had ever smoked cigarettes; and 14.1 percent had ever used smokeless tobacco. In the past month, the rates of use were 50.9 percent for alcohol, 27 percent for cigarettes, and 3.4 percent for smokeless tobacco. Extensive tables and appended supplementary data