The intratracheal delivery of glutathione (GSH), in liposome-encapsulated form, prolongs retention of the drug in the rat lung. This study has been designed to determine the extent and time-course of pulmonary tissue uptake of administered 14C-labelled liposomes containing [3H]GSH. Liposomes, composed of dimyristoylphosphatidylcholine (DMPC), dipalmitoylphosphatidylcholine and distearoylphosphatidylcholine each with or without 30 mol% cholesterol showed a clearance greater than 80% from the bronchoalveolar lavage, 24 h after intratracheal instillation. Lung tissue content of 14C-lipid increased with time: by 72 h, 42-56% of the administered dose was recovered from the tissue. [3H]GSH was present in pulmonary tissue in relatively constant amounts throughout the 72 h, ranging from 14-35% of the administered dose. Vesicles composed of DMPC had a low entrapment for GSH. There were only minor differences in GSH entrapment efficiency and lung tissue uptake between vesicles of the other lipid compositions.