We report a prospective evaluation of three human, continuous colorectal cancer cell lines and a new semiautomated radiometric technique (Bactec system) as a primary screening procedure for cytotoxic compounds with activity against cancer of the large bowel. COLO 320DM, Ht-29, and the metastatic OM-1 colon cancer cell line that have previously been shown to yield clinically relevant information in terms of drug sensitivity patterns in humans were all tested against 11 new compounds currently being investigated in phase I or early phase II clinical trials. Our results suggest that trimetrexate, DUP-785, didemnin B, and flavone-8-acetic acid may be clinically effective for the treatment of colorectal cancer.