Isotopic techniques enable to determine the best conditions to aerosolize pentamidine as a preventive treatment of pneumocystis. An original labelling technique of pentamidine isethionate has led into a feasibility study of pentamidine scintigraphy in the monkey, and then to a clinical study. A tracer dose of 2 mg of pentamidine isethionate was diluted into 200 mg of pentamidine mesylate. An ultrasonic nebulizer (TV 6000) and a jet nebulizer (Venticis II) were first compared in four baboons. With the two nebulisers the curves of pulmonary kinetic activity showed a peak 10-15 minutes after the beginning of inhalation and then a plateau. With the ultrasonic TV6000 the pulmonary dose was on average 0.8 mg or 0.4% of the pentamidine aerosolized and the gastric contamination 3.1%. With the Venticis II compressed air apparatus the amount of pentamidine delivered to the deep lung was a mean of 4.2 mg or 2.1% of the aerosolized dose whereas the gastric contamination was only 0.5%. The delivery of the aerosol by the ultrasonic inhaler TV 6000 was then compared with two compressed air inhalers Venticis II and Respirgard II in four patients infected with HIV virus who were submitted to a preventative therapy against pneumocystis. With the ultrasonic TV 6000 the pulmonary dose was 0.8 mg or 0.3%-0.5% of the dose of pentamidine aerosolized and the digestive contamination was 3.1%. The performance of the two compressed air nebulizers Venticis II and Respirgard II were similar. The amount of pentamidine delivered to the deep lung was respectively 12 and 14 mg or 6 and 8% of the dose of pentamidine aerosolized and the digestive activity was 0.2%.(ABSTRACT TRUNCATED AT 250 WORDS)