Glutathione, as the chief nonprotein intracellular sulfhydryl, affects the efficacy and interactions of a variety of antineoplastic interventions, mainly through nucleophilic thioether formation or oxidation-reduction reactions. Thus, glutathione plays a role in the detoxification and repair of cellular injury by such diverse agents as mechlorethamine, melphalan, cyclophosphamide, nitrosoureas, 6-thiopurine, 4'-(9-acridinylamino)methanesulfon-m-anisidide, the quinone antibiotics (including Adriamycin, daunorubicin, and mitomycin C), the sesquiterpene lactones (such as vernolepin), and other sulfhydryl-reactive diterpenes (like jatrophone). Glutathione may play a similar role in host and tumor cell responses to radiation, hyperthermia, and the reactive reduction products of oxygen secreted by inflammatory cells. Further, glutathione participates in the formation of toxic metabolites of such chemotherapeutics as azathioprine and bleomycin and may affect the cellular uptake of other agents, such as methotrexate. It seems likely that alterations in glutathione metabolism of tumor or host as a result of one therapeutic intervention may affect the outcome of concurrent treatments. Knowledge of these interactions may be useful in designing combination therapy for neoplastic disease.