Tegafur is a prodrug of the antineoplastic agent fluorouracil, and is administered in a 1:4 molar ratio with the fluorouracil modulator uracil. Oral tegafur/uracil 300 mg/m(2)/day plus calcium folinate 75 or 90 mg/day for 28 days every 35 days was as effective as intravenous (IV) fluorouracil 425 mg/m(2)/day plus folinic acid 20 mg/m(2)/day for 5 days every 28 or 35 days in the treatment of patients with metastatic colorectal cancer in two large, randomised, nonblind, multicentre trials (n = 816 and 380). Median survival time among patients treated with tegafur/ uracil or fluorouracil was approximately 12 months in both trials. Results from both trials also demonstrated no significant between-group differences in overall response rates among patients treated with oral tegafur/uracil (12 and 11%) or IV fluorouracil (15 and 9%). In elderly patients (aged > or = 70 years) with metastatic colorectal cancer, results from small noncomparative studies showed that treatment with oral tegafur/uracil afforded overall response rates of 12.5 to 29% and was well tolerated. During preoperative treatment with oral tegafur/uracil plus calcium folinate as an adjunct to radiotherapy in patients with stage II or III rectal cancer, the maximum tolerated dosage of tegafur/uracil was 350 mg/m(2)/day (administered 5 days per week for 5 weeks). Among the 15 patients who were followed for 5 to 8 months, three had a complete response to treatment. Treatment with tegafur/uracil was also given postoperatively. The most common adverse events associated with oral tegafur/uracil were anaemia, nausea/vomiting, diarrhoea, thrombocytopenia, mucositis, neutropenia, asthenia, anorexia and abdominal pain. Oral tegafur/uracil was associated with a significantly more favourable tolerability profile than IV fluorouracil in the two large randomised trials. In particular, stomatitis and most adverse haematological events were less frequent.