Administration of more than 40 separate pharmacologic agents has been associated with some form of pulmonary toxicity. This problem is becoming more significant every year. Occasionally, effective modes of therapy must be withdrawn because of undesirable pulmonary side effects, putting patients at risk for potentially lethal diseases. Pulmonary parenchymal damage due to drugs is an especially troublesome problem because irreversible pulmonary disease may occur. Mechanisms of pulmonary parenchymal tissue damage by drugs are unclear. It appears that some drugs induce direct tissue injury in addition to indirect tissue damage through amplification of pulmonary inflammation; other drugs cause pulmonary alterations soley through indirect mechanisms. Common clinical syndromes associated with drug-induced pulmonary parenchymal disease include (1) pneumonitis/fibrosis, (2) hypersensitivity lung disease, and (3) noncardiogenic pulmonary edema. Less common patterns of pulmonary parenchymal injury by drugs include bronchiolitis obliterans and a pulmonary renal syndrome. Risk factors for pubnonary injury due to pharmacologic agents are partially defined but not entirely understood. To date, there are no adequate tests for early detection of pulmonary damage by drugs, although research into this area is active. This review discusses mechanisms and clinical features of drug-induced pulmonary parenchymal injury to aid the clinician in recognizing and understanding these syndromes. © 1987.