Information was obtained on the number of State inmates with substance problems who need drug treatment and the number who receive such treatment, provisions for drug treatment by State prisons and arrangements for continuous care for inmates after their release, and obstacles to providing drug treatment in State prisons. The GAO estimated that over 500,000 of 680,000 State inmates nationwide may have drug abuse problems but determined that State prisons can only provide drug treatment to about 100,000. Many State prisons attempt to optimize their treatment capacity by targeting more intensive treatment to inmates nearing release. Even so, many inmates are released without receiving any drug treatment services. Recognizing the need to enhance prison drug treatment services, several States are expanding or improving their prison treatment programs. Services available in these programs are mixed and include drug education, self-help, professional counseling programs, intensive residential treatment programs, and programs that provide aftercare upon release. States face several challenges in enhancing their drug treatment services: limited funding, security considerations, and difficulties in assuring the availability of aftercare. Additional information is appended on prison drug treatment programs, Federal funding for implementing State prison drug treatment programs, and elements of prison drug treatment programs in five States (Louisiana, Michigan, New York, Washington, and Wisconsin). 2 tables and 2 figures