In this study, the safety with efficacy of infusional 5-fluorouracil (5-FU) (200 mg/m2/day) combined with subcutaneous interleukin-2 (IL-2) (9-27 x 10(6) IU/day) was investigated in patients with metastatic and renal cancer. In the 24 patients evaluated, the overall response rate was 17% (1 CR, 3 PR). The major toxicity was the vascular leak syndrome (VLS) which required inotrope support in 18% of treatment cycles. Other common systemic toxicities were vomiting, oedema and malaise (grades 1 and 2). There was no enhanced or novel toxicity from the combination of drugs. Based on this study, it will be feasible to use infusional chemotherapy with other cytokine combinations.