Chronic treatment with Sasa Health, extract of bamboo grass leaves obtained by alkaline hydrolysis, in drinking water at the concentration of 0.044%-0.088% Fe-Chlorophyllin Na resulted in the significant inhibition of both development and growth of spontaneous mammary tumours in a high mammary tumour strain of SHN virgin mice. Limited treatment for 12 days in mice with palpable sizes of mammary tumours also markedly retarded the growth of the tumours. The end-bud formation and thymidylate synthetase activity of normal mammary glands were stimulated, but the formation of preneoplastic mammary hyperplastic alveolar nodules was inhibited by the treatment. Chronic ingestion of Sasa Health stimulated the excretion of urine components and decreased and increased the prolactin level and superoxide dismutase activity in serum, respectively. It showed no deleterious effects on food and water intake, body growth and any external appearance and all findings indicate that Sasa Health could be a promising agent for the protection and therapy of breast and other types of tumours.