Copovithane (BAY i 7433), a copolymer of 1,3-bis(methylaminocarboxyl)-2-methylenepropanecarbamate and N-vinyl pyrrolidone, has antitumor activity in vitro and in vivo. The mechanism of this polymer is unknown. Thirty patients with advanced colorectal carcinoma with measurable tumors were treated in an open randomized study with two schedules of copovithane (schedule A: 6 g/m2 i.v. over 30 min daily for 5 consecutive days and repeated every 3 weeks; schedule B: 10 g/m2 i.v. over 30 min once a week until progression, unacceptable toxicity, or up to 18 months). Fifteen patients received copovithane on a weekly schedule, and 15 patients received it on an intermittent schedule. None of the patients on either schedule achieved a complete or partial remission. Copovithane was ineffective against colorectal carcinoma by both schedules selected in this study.