Aqueous extracts from the vegetative submerged mycelia of cultivated Basidiomycetes Ganoderma lucidum, Lentinus edodes, and Grifola frondosa, as well as from the fruiting bodies of G. lucidum, were found to have antitumor activity. The antitumor effect of the mycelial extracts from all 3 fungal species was ascertained in vivo in rats with implanted kidney cancer. Dystrophic changes in tumor cells and tumor necrosis (up to 90%) were noted. In vitro cytotoxicity studies of the A549 human lung adenocarcinoma cell line and HEp-2 human laryngeal epidermoid carcinoma cells showed that the extracts from the G. lucidum fruiting bodies and from the L. edodes vegetative mycelium were the most effective. The animals' immune systems were activated, and the fungal extracts displayed no toxicity when administered orally.