A phase I study of recombinant human tumor necrosis factor (rHu-TNF:PT-050) given by intravenous infusion over 30 min or by intratumoral administration was performed in 53 patients with various types of malignant tumors. The dose of rHu-TNF was started with 0.1 x 10(6) U/body for both intravenous infusion and intratumoral administration and increased to 5 x 10(6) U/body for intravenous infusion and 2 x 10(6) U/body for intratumoral administration. The side effects of rHu-TNF given by intravenous infusion included fever, shaking chills, hypotension, general malaise, nausea, and vomiting, and clinical laboratory tests showed elevations of GOT, GPT, and ALP, etc. Among these, only hypotension was dose-related and was considered to be a dose-limiting factor. The maximum tolerable dose estimated was 1 x 10(6) U/body. The plasma concentration of rHu-TNF after completion of a 30-min infusion was dose-dependent, and the elimination half-life was 0.5-2.4 hr. When the rHu-TNF was administered intratumorally, the frequency of side effects was low compared with intravenous infusion.