PIP: Major interventions to reduce HIV transmission involve increasing knowledge about preventing HIV transmission for sustained behavioral changes; and enhancing the control of sexually transmitted diseases (STD), which increase the probability of HIV transmission. Activities have also been developed to prevent the transmission of HIV by blood, donor selection, and more rational use of transfusions. Behavioral changes among injecting drug users have also been promoted. Recommendations are made for the evaluation of AIDS programs, focusing on prevention of sexual transmission of HIV, and outlining the approach developed by the Global Program on AIDS (GPA; Geneva, Switzerland) for use by national programs. Based on the feasibility, accuracy, reliability and validity of the quantitative assessment of programs, 10 indicators of progress and outcomes of prevention activities have been developed by GPA. These include indicators of population knowledge regarding preventive practices, reported sexual behavior and use of condoms in the general population, STD service evaluation, and indicators of program impact. The latter are measured through the reported STD incidence in the general male population, and syphilis and HIV prevalence in women. The four methods are proposed for measuring the 10 core prevention indicators (PI). Five PIs are measured during a population survey: reported knowledge of preventive practices (PI-1), condom availability at peripheral level (PI-3), reported frequency of nonregular sexual partners (PI-4), reported condom use during nonregular sexual encounters (PI-5), and reported STD incidence among men (PI-9). Condom availability at central level (PI-2) is assessed through key-informant interviews with major distributors. Structured health facility surveys allow assessment of the appropriateness of STD case management (PI-6 and PI-7). A serosurvey among antenatal clinic attenders aged 15-24 years allows the measurement of HIV and syphilis seroprevalence in that population (PI-8 and PI-10). GPA recommends that such surveys be repeated after a period of 1 to several years.