Fifty-seven patients with advanced measurable or evaluable colorectal cancer not previously treated with chemotherapy and tumor manifestations from colorectal cancer were treated with tauromustine (TCNU), a new nitrosourea with a therapeutic index against murine tumors better to or equal to that of the established nitrosoureas. The dose was 130 mg/m2 orally q 5 weeks. There were one CR and seven PR, for an overall response rate of 14%. Responding sites included the liver (one CR and two PR), lung (four PR) and lymph nodes (two PR). The median duration of response was 33+ weeks (21+ to 34 weeks). The main dose limiting toxicity was myelosuppression which seemed to be cumulative. Subjectively, the drug was well tolerated although most patients experienced nausea and vomiting for some hours. It is concluded that TCNU is a well tolerated compound with limited, but definite antitumor activity against colorectal cancer and that further studies in this disease could be of interest.