Overviews discuss the impacts of HIV on scientific research, medicine, planning for public health responses, and direct work with drug users and the need for new interventions to strengthen both the primary prevention of drug-injecting behavior and the secondary transmission of HIV. Additional papers focus on the clinical features of HIV infection and AIDS in drug users, HIV antibody testing, the neuropsychiatric complications of HIV infection, trends in drug abuse and high-risk behavior, and HIV transmission and prevention efforts in several cities. Other papers discuss HIV prevention programs and policies in individual countries, AIDS in correctional facilities, needle exchange programs, counseling of drug abusers, self-help programs, the primary care of HIV-positive drug abusers, and the role of the therapeutic community. Examples are presented from the United Kingdom, the United States, Italy, Australia, and other countries.