Excluding growth in total clients over time, broad characteristics of providers and clients showed either stability or gradual change between 1980 and 1994. Large differences existed among the States in the number of clients in treatment as a proportion of the general population, in patterns of substances abused by clients, and in the mix of outpatient versus 24-hour care. Across the country, there were an estimated 943,000 clients in specialty substance abuse treatment on October 1, 1994. Whites accounted for the largest estimated share of clients, followed by Blacks and Hispanics. The racial and ethnic composition of clients changed little between 1980 and 1994. There was an increase in the proportion of women in treatment, and there was a gradual aging of clients in treatment. Outpatient services accounted for an estimated 87 percent of all clients. Notes, figures, tables, references, appendixes