Measures aimed at preventing complications and slowing progression of type-1 human immunodeficiency virus (HIV-1) can potentially reduce morbidity. Although little is known about the use of such measures, such data are critical for program planning. This study was performed to quantify the frequency and patterns of use for such interventions. We enrolled 1,171 persons infected with HIV, but without an acquired immunodeficiency syndrome (AIDS) defining diagnosis, in a multicenter prospective study of the pulmonary complications of HIV infection. Participants were homosexual/bisexual men, injection drug users (IDUs), or female sexual contacts of HIV-infected men. Centers were university-based and geographically dispersed across the United States. Standardized questionnaires were administered on entry and at three-month or six-month intervals; we correlated use of general and HIV-related preventive measures before entry and during the first three years in study with clinical/epidemiologic characteristics. Overall use of preventive interventions was low; only one third of study entrants had used such measures. Use was greatest among those with advanced HIV infection, but only half used preventive measures on entry; IDUs were less likely than homosexuals to use these services. Although use of interventions such as anti-Pneumocystis and antiretroviral agents increased during study participation, general measures such as pneumococcal vaccine and tuberculosis prophylaxis were used by less than 30% of those eligible for use. Among IDUs, cumulative use of these measures remained below 20% during the first three years of this study. We conclude that HIV-infected persons underuse preventive interventions, particularly general measures. Although IDUs are especially unlikely to receive preventive interventions, homosexual/bisexual men and female partners also appear to underuse preventive measures. Strategies for enhancing the use of preventive intervention are needed.