The current study was initiated to confirm preliminary reports that 20% or more of patients with colorectal cancer who fail treatment with 5-fluorouracil (FUra) will respond to treatment with either leucovorin plus FUra or with sequential methotrexate, FUra, leucovorin. One hundred two patients with advanced, measureable colorectal cancer who failed treatment with FUra and/or 5-fluorodeoxyuridine (FUdR) were randomized to treatment with either high-dose leucovorin plus FUra (Arm B) or sequential methotrexate, FUra, leucovorin (Arm C). In this interim report, 92 patients were evaluable for toxicity and 89 patients were evaluable for response. Grade 3 or 4 nonhematologic toxicity which was primarily gastrointestinal was experienced by 25% of patients on both treatment arms during at least 1 treatment cycle. Hematologic toxicity was minimal. Among 43 evaluable patients on Arm B, there were 2 complete responses (5%) and 1 minor response (3%). Among 46 evaluable patients on Arm C, there was 1 complete response (2%), 1 partial response (2%), and 6 minor responses (14%). The median time to treatment failure was 2.2 months on Arm B and 3.5 months on Arm C. The median survival was 8.3 months on Arm B and 8.7 months on Arm C. Colorectal cancers that are resistant to FUra are cross-resistant to both experimental combinations.