A phase II study was performed to assess the efficacy and toxicity of UFT (tegafur-uracil in the molar ratio 1:4) modulated with leucovorin (LV) in previously untreated patients with advanced colorectal carcinoma (CRC). 79 patients with measurable advanced colorectal cancer (CRC) and no prior chemotherapy were included. 75 patients were evaluable for toxicity and response. The regimen consisted of LV 500 mg/m2 administered intravenously on day 1, followed by oral UFT 390 mg/m2 on days 1-14. Patients received oral LV 15 mg every 12 h on days 2-14. Treatment was repeated every 28 days for a minimum of four courses per patient. Three hundred and ninety-eight cycles of chemotherapy were delivered (median five per patient). 7 patients (9%) had a complete response, and 22 a partial response for an overall response rate of 39%. Mild gastrointestinal toxicity was dose limiting: grade 3-4 diarrhoea appeared in 9% of patients. Other grade 3-4 toxicities were nausea/vomiting and mucositis in 4% of patients, gastric pain and leucopenia in 3%. Oral UFT modulated by oral LV is active in advanced CRC and can be administered on an outpatient basis with no significant toxicity requiring hospitalisation. Given its excellent tolerance profile and low toxicity, the regimen should be thoroughly studied and compared with 5-fluorouracil modulated by LV.