Administration of a number of cytotoxic agents has been associated with interstitial pneumonitis, alveolitis and pulmonary fibrosis. Some (bleomycin, busulfan, methotrexate) are well known to cause this problem, and others (carmustine, semustine, zinostatin, mitomycin, and chlorambucil) have only recently been recognized to do so. We review and update the available information about this form of drug toxicity. Interaction between these drugs and thoracic radiation or high oxygen fractions in inspired air has produced pneumonitis at doses lower than when the drug is used alone. Synergism between the drugs themselves when given concurrently also produces pulmonary toxicity at lower doses. With some drugs and in some patients steroids will diminish the pulmonary abnormalities, but death from hypoxia is a frequent outcome. Since early recognition of the problem and withdrawal of the injurious agent is the best treatment, physician awareness of and alertness to this toxicity and its relative risk is most important. The discovery of analogs of bleomycin with a better therapeutic index, specifically reducing pulmonary damage, is one of the goals of current cancer drug development.