Tumor necrosis factor (TNF) has demonstrated antitumor activity against a variety of tumors and is particularly cytotoxic to capillary endothelial cells, which are the presumed cell of origin of Kaposi's sarcoma. We evaluated the toxicity and clinical antitumor and antiretroviral effects of recombinant TNF administered at a once weekly dose of 100 micrograms/m2 intravenously for 8 weeks in five men with AIDS-related Kaposi's sarcoma and without prior opportunistic infection. One patient was removed from study at week 4 due to rapid progression of Kaposi's sarcoma, another patient with stage IV disease and a pretreatment CD4 count of 11 developed fever, hypotension, and pneumonia at week 7 and died 8 days after discontinuing recombinant TNF. No pathogenic organisms were isolated. He had marked eschar formation of his Kaposi's sarcoma lesions, particularly in areas previously exposed to radiation therapy. Uniform toxicities included fevers, rigors, and headaches during drug infusion that were ameliorated by prophylactic meperidine hydrochloride and acetaminophen. All experienced fatigue and three had arthralgias. One patient had transient hypotension which corrected with i.v. fluids. No significant hematologic, hepatic, or renal toxicities were seen. All patients had some progression of their Kaposi's sarcoma on study. There was no change in CD4 or CD8 count or in CD4:CD8 ratios. Serum human immunodeficiency virus (HIV) p24 antigen levels increased greater than 50% in three patients. We conclude that, as a single agent, at a dose of 100 micrograms/m2 recombinant TNF by i.v. infusion has no obvious antitumor or antiretroviral effects in patients with AIDS-related Kaposi's sarcoma.