To examine the effects of combination therapy with traditional Chinese preparations (Syô-saiko-tô, Zyûzen-taiho-tô orCinnamomumcortex) and OK432 or mitomycin C on the antitumor activities and TNF producibility, an investigation was carried out using mice transplanted with Ehrlich or Meth A tumor cells. Development of the transplanted tumors was strongly inhibited by the combination therapy, and the tumor necrosis factor (TNF) producibility was increased with the combination of a traditional Chinese preparation and OK432. A significant negative correlation was observed between the TNF activities and tumor weight, and there was a positive correlation between the TNF activities and spleen weight in the Ehrlich-bearing DDY mice receiving traditional Chinese preparations or OK432. Marked lymphocytosis, hyperplasia, and hypertrophy of Kupffer's cells in the liver were noted in the tumor-bearing DDY mice receiving traditional Chinese preparations or OK432. In two-step carcinogenesis experiments involving treatment with DMBA and TPA to induce skin papillomas, Zyûzen-taiho-tô appeared to be effective in inhibiting carcinogenesis. These results suggest that the antitumor activities and capacity for TNF production of the preparations are probably due in part to stimulation of the reticuloendothelial system, including macrophages, and induction of a host-mediated antitumor substance like TNF as one of the immunopotentiators.