Sixty-six patients with disseminated malignancy were treated with recombinant interleukin-2 (IL-2) on a three times a week (M, W, F) IV-bolus injection schedule. Doses ranged from 0.001 to 14.0 x 10(6) units/M2 body surface area. Consecutive groups of 3-5 patients were placed on each dose level and were maintained on that level except for dosage de-escalation for toxicity. Toxicity to all major organ systems were noted with major toxicity including fever and chills, anorexia, fatigue and malaise, arthralgias and arthritis as well as hepatic and renal toxicity. All toxicity reversed within one week of drug cessation. Renal toxicity manifested by azotemia, arthritis and fatigue were the common dose limiting toxicities and the maximally tolerated dose was 12 x 10(6) units/M2. Pharmacokinetic studies indicated a short half-life (T1/2 alpha = 7-23 minutes). At doses over 0.5 x 10(6) units/M2 increases in absolute lymphocytes and eosinophil counts were noted. All T lymphocyte subsets increased. Maximal increases were seen at 4-8 x 10(6) units/M2 with a lesser increase at 10-14 x 10(6) units/M2 dosage level. Circulating NK cells also increased while circulating LAK cells were detected during therapy. Partial responses were noted in 3 patients with melanoma. These lasted 4, 6 and 16 months and involved pulmonary, pulmonary plus mesenteric and retro-orbital plus hepatic metastases respectively in these patients.