To investigate the effect of paraquat-induced lung damage on pulmonary absorption of drugs, rats were given a single oral dose of paraquat (250 mg/kg), and rates of drug absorption from damaged and control lungs were compared after various times. To measure absorption rates of drugs, 0.1 ml of 10 mM drug solution was administered through a tracheal cannula to anesthetized animals and, after various times, lungs were assayed for unabsorbed compound. Drugs investigated were procaine amide ethobromide, p-aminohippuric acid, and procaine amide. Rates of drug absorption increased 1.4-2.8-fold at 3.5 days after paraquat administration and returned to near control values by the 15th day. The results suggest that paraquat-induced lung damage increases the porosity of the pulmonary epithelium.