A phase I trial of repetitive weekly cycles of human recombinant interleukin-2 (IL-2) was performed in 23 patients with metastatic carcinoma. Patients received 4 days of IL-2 each week, followed by 3 days of observation, for 4 consecutive weeks. IL-2 was administered iv at 1.0 or 3.0 X 10(6) U/m2/day by one of three schedules involving continuous or bolus infusions. All treatment was carried out in a general hospital ward without intensive care unit monitoring or support. Seventeen patients had metastatic renal cell carcinoma; three of these demonstrated measurable (greater than 50% shrinkage) partial responses. This study demonstrates that IL-2 given alone without lymphokine-activated killer cells in this manner can induce antitumor effects with acceptable toxicity.