Eight species of novel recombinant tumor necrosis factor-S (rTNF-SAMgroup) were constructed in which N-terminal amino acid sequences were based on that of TNF-S from THP-1 cells with higher basicity than conventional rTNF-α. Two of this rTNF-SAMgroup, denoted as rTNF-SAM1and rTNF-SAM2, showed more cytocidal activity on A549 lung carcinoma cells and G401 Wilm's tumor cells than did rTNF-α. In addition to these cell lines, rTNF-SAM1revealed strong cytocidal activity on T24 bladder carcinoma cells, which are resistant to rTNF-α. Moreover, possible cachectin activity of rTNF-SAM2seemed to be lower than that of conventional rTNF-α, suggesting that rTNF-SAM2has less side effects. Actually, toxicity as expressed by LD50value of rTNF-SAM2as well as others of the rTNF-SAMgroup was significantly lower than that of conventional rTNF-α. Thus, newly constructed rTNF-SAM1and rTNF-SAM2should be more promising antitumor reagents for clinical use, since they were shown to be superior to conventional rTNF-α both in antitumor effect and in less side effects.