Seventy-five previously untreated patients with measurable advanced colorectal cancer were treated with 5 fluorouracil 1,000 mg/m2 as a 24-hour intravenous (i.v.) continuous infusion during days 1-5 and 28-32 every cycle, plus 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU), 200 mg/m2 i.v. bolus on day 1, all given every 8 weeks up to 6 cycles. Median Karnofsky performance status (KPS) was 100. Sites of disease at entry were mainly the abdomen (45%) and liver (33%). All patients were evaluable for response and survival. There were two complete responses and seven partial responses (PR) for an overall response rate of 12% (95% confidence limits: 5-20%). Four out of 25 patients with liver metastases alone had PR. Stabilization was seen in 40 patients (53%). Median time to progression was 9.3 months and overall median survival was 12.5 months, whereas median survival for patients with liver metastases alone was 16 months. Toxicity was mild except for 8% with WHO grade 4 mucositis. Only KPS had statistical significance in the multivariate analysis of prognostic factors. It is concluded that this regimen is relatively active and well tolerated in patients with advanced colorectal cancer.