Tumor necrosis factor is a cytokine derived from activated macrophages. This agent is cytostatic and cytolytic against transformed human cell lines in vitro and has in vivo activity against a variety of murine tumors. We report a clinical study of the pharmacokinetics, toxicity, and biological activity of i.v. and i.m. administered recombinant human tumor necrosis factor (rTNF). Twenty patients with metastatic cancer were given rTNF in doses ranging from 1 to 200 micrograms/m2 by alternating i.m. and i.v. bolus injections with a minimal intervening period of 72 h. Each patient received a maximum of eight treatments given twice weekly over a 4-week period. With i.v. bolus administration, serum concentrations of rTNF were detected by enzyme-linked immunosorbent assay at doses of 25 micrograms/m2 or greater. The clearance of rTNF in the serum was described by a monoexponential equation with a half-life calculated to be 14-18 min. After i.m. administration, serum concentrations of rTNF were consistently detected by enzyme-linked immunosorbent assay at doses of 150 micrograms/m2 or greater. Peak concentrations were observed within 2 h and rTNF was occasionally detected, at the lower limit of sensitivity of the assay, at 24 h postinjection. rTNF was well tolerated clinically in this dose range, and there was evidence of antitumor effect.