A total of 16 patients with histologically confirmed colorectal cancer were entered into this phase II trial, designed to evaluate the efficacy and safety of tallysomycin S10b. The compound was given i.v. weekly at a dose of 2.5 mg/m2 by push injection. Pulmonary toxicity was the most significant side effect; it was observed in three patients and required treatment discontinuation in one. Skin lesions occurred in three patients. Other side effects were mild and their relationship to drug administration was ill-defined. No responses were observed in this group of patients, most of whom had received prior therapy.