The Safety and Effectiveness of Pentamidine in the Prevention of Pneumocystis Carinii Pneumonia (PCP) in Patients With AIDS Who Have Had PCP Before

Inclusion Criteria Concurrent Medication: Allowed: * Zidovudine (AZT). Exclusion Criteria Co-existing Condition: Patients with the following are excluded: * Requiring ongoing active therapy for an opportunistic infection (O.I.) at time of entry or those with either of the following AIDS-defining O.I.'s prior to entry: * Toxoplasmosis. * Cryptococcosis. * Transfusion dependent (requiring blood transfusion more than once per month). The last transfusion cannot have been given within 7 days of study entry. * Pulmonary Kaposi's sarcoma (KS). * Asthma requiring medication. * Active therapy for tuberculosis. Concurrent Medication: Excluded: * Active therapy for tuberculosis. Patients with the following are excluded: * Requiring ongoing active therapy for an opportunistic infection (O.I.) at time of entry or those with either of the following AIDS-defining O.I.'s prior to entry: * Toxoplasmosis. * Cryptococcosis. * Transfusion dependent (requiring blood transfusion more than once per month). The last transfusion cannot have been given within 7 days of study entry. * Pulmonary Kaposi's sarcoma (KS). * Unwilling to sign informed consent. * Cannot cooperate with study procedures. * Asthma requiring medication. Prior Medication: Excluded within 30 days of study entry: * Antiretrovirals other than zidovudine (AZT). * Immunomodulating agents. * Corticosteroids. Patients must: * Have AIDS and recovered from their first episode of cytologically or histologically proven Pneumocystis carinii pneumonia (PCP). * Be at least 2 weeks and no more than 24 weeks status post therapy for acute PCP. * Have positive antibody to HIV by any federally licensed ELISA test kit, or confirmed Western blot test. * Have adequate pulmonary function (vital capacity = or \> 80 percent of predicted; forced expiratory volume (FEV), 1 s = or \> 65 percent of total FEV; and corrected pulmonary diffusion capacity \> 60 percent of predicted). * Free of acute medical problems. Active substance abuse.