Criteria for treatment are to need it and to be within 1 year of release. The 'in need' population was estimated by examining the records of a sample (265) of inmates released in the 4 months prior to the start of treatment services. This sample will later serve as the control group for determining the impact of treatment services on program participants. Over 80 percent of the sample had drug abuse histories, indicating that approximately 2,000 inmates will need drug treatment annually. The random sample was also used to explore any relationships between prison behavior, criminal behavior, and drug abuse. There was no relationship between substance abuse and offense of incarceration, but drug abusers had more drug-use infractions in prison. Abusers had no more total infractions than nonabusers. An assessment of the treatment process found that 774 persons were admitted to the program in the first year's operation. All were screened with standardized assessment instruments prior to admission. The overrepresentation of women in the treatment population was the only evidence of selection discrimination. There were substantial differences in the treatment hours per week across services in the four catchment areas, ranging from a high of 13.3 hours to a low of 1.4 hours. A total of 570 of the 774 admissions completed treatment, nearly four times the expected completion rate. Program impact on participants' in-prison behavior and recidivism after release will be measured in a subsequent study. 31 tables and 6 figures.