Vintriptol, a tryptophan ester of vinblastine, is a new vinca alkaloid derivative. Preclinical studies have demonstrated its antitumour activity in a large variety of animal models. In this phase I study, 47 patients with advanced cancer were exposed to escalating doses of vintriptol, starting at 6 mg/m2 and following a modified Fibonacci schedule. The drug was administered as an intravenous push on a weekly schedule. Myelosuppression was the dose-limiting toxicity and the maximum tolerated dose was 45 mg/m2. Other toxicities consisted of mild nausea and vomiting and the occurrence of fever and dryness of the mouth immediately after drug administration. Neurotoxicity, a major side-effect of other vinca alkaloids, was insignificant. 1 partial remission in a patient suffering from colorectal cancer and 1 minor response in a patient with a metastatic tumour of the cutaneous appendagous glands were documented. Pharmacokinetics of vintriptol were evaluated at the highest dose levels. A dose schedule of 40 mg/m2 vintriptol per week is recommended for phase II studies.