A Double-Blind Group Comparative Study To Evaluate the Long-Term Safety and Effectiveness of Two Different Doses of Aerosol Pentamidine in the Prophylaxis of Pneumocystis Carinii Pneumonia in AIDS Patients With Multiple Episodes of PCP

Inclusion Criteria Concurrent Medication: Allowed: * Zidovudine (AZT). Patients must have: * AIDS. * Recovered from their most recent episode of Pneumocystis carinii pneumonia (PCP). Patients must be at least 2 weeks status post therapy for acute PCP. * Adequate pulmonary function (vital capacity = or \> 65 percent of predicted; forced expiratory volume, 1 s = or \> 55 percent of total FEV; and corrected pulmonary diffusion capacity \> 50 percent of predicted). * Patients must be free of acute medical problems. Exclusion Criteria Co-existing Condition: Patients with the following are excluded: * AIDS-defining opportunistic infection prior to entry such as toxoplasmosis and cryptococcosis. * Pulmonary Kaposi's sarcoma. * Asthma poorly controlled by medication. * Receiving 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 at time of study entry. * AIDS-defining opportunistic infection prior to study entry such as toxoplasmosis and cryptococcosis. * Pulmonary Kaposi's sarcoma. * Unwilling to sign informed consent. * Asthma poorly controlled by medication. * Unwilling to cooperate with study procedures. * Receiving active therapy for tuberculosis. Prior Medication: Excluded within 30 days of study entry: * Antiretrovirals (other than zidovudine (AZT)). * Immunomodulating agents. * Corticosteroids. Prior Treatment: Excluded within 7 days of study entry: * Transfusion. * Patient cannot be transfusion dependent (requiring blood transfusion more than once per month). Active substance abuse.