Thirty-eight patients with advanced colorectal adenocarcinoma were entered on a phase II trial of 5-fluorouracil (5-FU) in continuous infusion, using a portable pump. Half of the patients had been pretreated (n = 19) and 16 of them had received intravenous bolus 5-FU alone or in combination. At the first cycle patients received continuous intravenous 5-FU at the dose of 650 mg/m2 per day for 7 consecutive days. Doses were escalated during the following cycles and adjusted according to the toxicities encountered in the previous cycle. Treatment was repeated every 3 weeks. A mean dose of 750 mg/m2/day (500-1,000) was administered for a mean number of 10 (1-25) cycles. We observed 1 complete response, 7 partial responses for a response rate of 21 +/- 13% (CI95%), 16 had stable disease (42%) and 14 a progression (37%). In 2 patients subsequently the residual tumors could be excised after chemotherapy. Median survival was 13.5 months. Toxicity was: grade 2 leukopenia in 1 patient (3%), mucositis grade 2-4 in 11 patients (29%), diarrhea grade 2-3 in 7 patients (18%), and hand and foot syndrome in 12 patients (31%). There was a correlation between the mean dose administered and the responses. However no clear correlation was found between toxicity and tumoral response for the first two cycles. These results confirm the limited efficacy of continuous intravenous 5-FU and its good tolerance in ambulatory patients.