Pneumocystis carinii pneumonia (PCP) is the most common serious infection in children with AIDS and is associated with a high death rate. Current approved treatment includes intravenous trimethoprim - sulfamethoxazole (TMP / SMX) and intravenous pentamidine, which are both effective in treatment of the first episode of PCP pneumonia. However, both therapies have a 50 percent or greater incidence of adverse reactions. Because of serious toxicities, drug treatment has had to be discontinued. Animal studies show that aerosolized pentamidine (pentamidine given through inhalation) is as effective as intravenous pentamidine. It is hoped that the aerosolized route will be less toxic than intravenous pentamidine. The study is the first step in evaluating the delivery of aerosolized pentamidine to children.