Antitumor effects of Royal Jelly (RJ) were investigated employing the transplantable tumors of mouse advance leukemia L1210 and P388 strains and Ehrlich, Sarcoma-180 ascites and solid tumor strains. RJ was administered orally in a prophylactic-therapeutic (30 days before and 30 days after the transplantations of tumor cells) or a therapeutic (30 days after the transplantations of tumor cells) manner. Tumor cells were transplanted i.p. (ascites tumor) or s.c. (solid tumor). The daily dose of RJ was 0 (control), 10, 100, or 1000 mg/kg. In the case of the therapeutic experiments employing advance leukemia L1210 and P388 strains, which gave quite a short survival period of 8 approximately 9 days, RJ did not show any antitumor effect. In the case of the therapeutic RJ application employing the Sarcoma-180 ascites tumor, which gave a moderate survival period of 16 days, the increased life span was 9.3 approximately 19.3%; and with the Ehrlich ascites tumor (survival period of 22.1 days), the increased life span was 20.4% (RJ 10 mg/kg . day) and 17.6% (RJ 1,000 mg/kg . day), but no antitumor effect was observed at the dose of 100 mg/kg . day. In the case of the therapeutic experiment employing Ehrlich solid tumor, tumor growth inhibition was 25.3 approximately 54.8%, where as the use of the prophylactic-therapeutic regimen gave a tumor growth inhibition of 38.3 approximately 45.7%. In the case of the therapeutic RJ application employing Sarcoma-180 solid tumor, tumor growth inhibition was 45.1 approximately 59.7%, where as the prophylactic-therapeutic regimen gave a tumor growth inhibition of 49.1 approximately 56.1%.(ABSTRACT TRUNCATED AT 250 WORDS)