Mitomycin C (NSC-26980) is a chemotherapeutic agent capable of producing objective regressions in gastrointestinal cancer at a rate approximately comparable to that of the fluorinated pyrimidines. It can be administered intravenously, with clinically tolerable toxicity, either by prolonged, low-dosage schedule or by a short, intensive course. The latter method presents fewer practical problems. The brief duration of tumor regressions obtained, the hazard of infiltration ulcers, and the compounding of toxicity with repeated treatment are factors which seriously limit the usefulness of the agent, however, and it cannot be recommended for routine clinical use.