Vinzolidine is a new, orally active, semisynthetic vinca alkaloid which shows broad antitumor activity against murine tumor test systems, This phase I study established a 1 day every 2 wk schedule of 35 mg/m2 in good-risk patients and of 30 mg/m2 in poor-risk patients. Maximal tolerated dose was 45 mg/m2 with severe neutropenia, syndrome of inappropriate antidiuretic hormone and paralytic ileus. Significant antitumor responses were seen in 2 patients with lymphoma and in 1 with squamous cell cancer of the lung.