Agaricus blazei Murill (Himematsutake) was found in the south-east Brazil and introduced to Japan. Although A.blazei is frequently used for cancer treatment, it is not known whether A.blazei is effective or not for cancer. Therefore it is important to provide proper information which help to understand its efficacy in man. Antitumor and antimetastatic activities of A.blazei were shown by different types of tumor bearing mice models in vivo. Although effects are weak, A.blazei possesses anti-inflammatory and antidiabetic activities. In F344 rat, its subchronical safety was proved by 90 days ingestion of 5% A.blazei extract containing diet. In dimethylnitrosamine induced hepatocarcinogenesis in rat, post administration of A.blazei did not block promoter step, indicating that A.blazei may not a multipotential and broad-spectrum edible item for cancer prevention. Furthermore, some studies in human indicate ineffectiveness of A.blazei to promote cancer cell elimination by chemotherapy. However, the same studies suggest beneficial effect of A.blazei to improve anorexia, vomiting and insomnia caused by chemotherapy. In conclusion, A.blazei is suitable not for elimination of cancer cells, but for reduction of adverse effects caused by chemotherapy in man.