The objective was to assess the efficacy of a biweekly dose of 60 mg aerosolized pentamidine (AP) for primary prophylaxis (PP) of Pneumocystis carinii pneumonia (PCP) and the impact of prophylaxis on survival in HIV-infected patients. Participants were AIDS patients with no history of PCP, patients with a CD4 count < or = 0.200 x 10(9)/L, or patients belonging to the CDC group IVC2, irrespective of CD4 count. It was an open, randomized, controlled trial. Patients were assigned to receive AP, 60 mg biweekly via a System 22 nebulizer, or to a control group not receiving any prophylaxis. Incidence curves for PCP and survival were generated using the Kaplan-Meier method, stratified by treatment group, and compared using the log-rank test. Data were analyzed according to intention to treat. There were 15 cases of PCP among 105 patients in the AP group and 32 cases among 104 patients in the control group. The cumulative incidence of PCP by 18 months was 13% (95% CI 5-21%) in the AP group and 30% (95% CI 18-41%) in the control group, (p = 0.002). During the study period 19 patients (18%) in the AP group died and 24 patients (23%) in the control group (NS; p = 0.28). We conclude that a biweekly dose of 60 mg AP is efficient as primary PCP prophylaxis when a System 22 nebulizer is used. There was, however, no difference in survival between the groups, suggesting that AP has an impact on morbidity only.