The use of aerosolized pentamidine was investigated in ten patients with the acquired immunodeficiency syndrome (AIDS) and Pneumocystis carinii pneumonia (PCP) who had previous or concurrent severe adverse reactions or contraindications to trimethoprim-sulfamethoxazole or parenteral pentamidine. A dose of 600 mg pentamidine in 6 ml sterile water, aerosolized in a small-particle producing jet nebulizer was administered for 25 minutes once daily for an average of 10.5 days to these ten patients. All patients improved their arterial O2 saturation and showed clinical and roentgenographic improvement within six to 21 days of aerosol pentamidine therapy. No adverse systemic reactions occurred. The results of this small open trial indicate that aerosolized pentamidine is effective and can be given safely to AIDS patients with PCP who have had adverse reactions to trimethoprim-sulfamethoxazole or parenteral pentamidine.