BACKGROUND Low-dose protracted continuous infusion (CI) 5-fluorouracil (5-FU), as proposed by Lokich et al, has been reported to be active and well tolerated in colorectal and breast cancers. We initiated a phase II trial with CI 5-FU in heavily pretreated undifferentiated carcinoma of the nasopharyngeal type (UCNT) patients in February 1989. METHODS Twenty-one UCNT patients with recurrent and/or metastatic disease were treated with CI 5-FU (300 mg/m2) for 6 consecutive weeks. Treatment was to be continued until disease progression. RESULTS Toxicity was mild. Diarrhea and mucositis (WHO grade 2 or greater) were seen in 4 (20%) and 6 patients (30%), respectively. Myelosuppression was infrequent, with only one patient with bone marrow invasion, experiencing grade 3 leukopenia. Two complete and 3 partial responses were obtained in 20 evaluable patients (ORR:25%). The median time to progression was 4 months (range 2-14); The median survival for the whole population was 10 months (avg 2-41). CONCLUSIONS This appears to be a useful palliative treatment for heavily pretreated UCNT patients.