A patient developed an interstitial pneumonitis while receiving chlorambucil for a chronic lymphocytic leukemia (cumulative dose, 8,340 mg). Withdrawal of drug treatment was followed by rapid improvement in the clinical condition. Bronchoalveolar lavage showed a T-lymphocytic alveolitis, whereas blood lymphocytes were predominantly of the B phenotype. The T-lymphocytic alveolitis persisted 6 weeks after drug therapy cessation with a predominant CD8+ phenotype, as observed in some hypersensitivity pneumonitis induced by drugs.