Two hundred consecutive bronchoalveolar lavages (BALs) performed at Mayo Clinic were retrospectively reviewed. The BAL specimens were evaluated for nuclear enlargement, hyperchromasia and increased cytoplasmic staining density as possible cytologic markers of cytotoxic drug effects. Of the 200 patients whose lavages were examined, 178 had sufficient clinical data for study. Thirty-six BAL specimens had cytologic changes consistent with drug-induced pulmonary toxic effects. Twenty-three of the 36 patients had concurrent or subsequent lung tissue available for evaluation; 10 of the 23 showed histologic evidence of cytotoxic effects. The results indicate that BAL is a safe and useful procedure, not only for the assessment of suspected pulmonary infection in immunocompromised patients, but also for the investigation of drug-induced pulmonary disease.