Summary: Nationwide, over 500,000 of the 680,000 state inmates may have substance abuse problems, but state prisons can provide drug treatment to just over 100,000. Most state prisons try to optimize their treatment capacity by targeting their more intensive treatment to those inmates nearing release. Even so, many inmates are released without receiving any drug treatment services. Recognizing the need to enhance their prison drug treatment services, the five states GAO visited are either expanding or improving their prison treatment programs. Services available in these programs were mixed--ranging from drug education, self-help, and professional counseling programs to more intensive residential treatment programs and programs that include aftercare upon release. Many challenges face states in enhancing prison drug treatment services, including limited funding, security considerations, and difficulties in making aftercare available. Prison officials said that they need more information and help from the federal government in implementing effective prison treatment programs. Federal officials with whom GAO spoke acknowledged this need and reported plans to aid the states.