To compare the use of pentamidine aerosol (inhaled mist) with the standard intravenous method of administration in patients with AIDS related Pneumocystis carinii pneumonia (PCP), to measure the amount of pentamidine aerosol that actually reaches the lung, and to see if close clinical observation is safer and as effective as drug therapy in the prevention of PCP recurrences. To compare the efficiency of 2 nebulizers - the Respirgard II nebulizer and the Cadema Aerotech II nebulizer. Aerosolized pentamidine was as effective as intravenous pentamidine in treating PCP in animals. More of the pentamidine reached the lungs and less was found in the liver and kidney after pentamidine was given by aerosol than after an intravenous injection. This suggests that the toxicity of pentamidine may be less if given by aerosol than if given by the intravenous route.