Thirty-five patients with previously untreated, advanced, measurable metastatic colorectal carcinoma were treated with a 12-week course of continuous 5-fluorouracil (5-FU) and weekly cisplatin. Twenty of 32 evaluable patients responded (five complete and 15 partial responses), for an overall response rate of 63% (90% confidence limits, 43%-75%). Toxicity was generally mild and reversible and included mucositis (40%), painful erythema of the palmar and plantar skin (30%), diarrhea (21%), nausea and vomiting (15%), and leukopenia (6%). One patient died of sepsis secondary to mucositis and myelosuppression. This program is a well-tolerated outpatient regimen for metastatic colorectal carcinoma. The response rate is higher than expected for 5-FU and cisplatin and suggests clinical therapeutic synergism at this dose rate and schedule.