Patients are evenly divided between two treatment arms to receive either aerosolized pentamidine every 4 weeks or dapsone orally three times weekly. Follow-up data is collected every 3 months, and patients are clinically evaluated every 6 months. Patients who develop PCP or a severe or persistent study drug toxicity may be switched to the alternative study drug at the clinician's discretion. Average duration of follow-up is 2 years.