The efficacy of infusion of black tea leaf, Camellia sinensis (Linn.) O. Kuntze (Theaceae), in reducing the cytotoxic effects of two heavy metal salts, chromium and arsenic, was tested in bone marrow cells of mice following dietary administration. Mice were given black tea infusion by gavage twice daily, in concentrations simulating human consumption, for 6 days. On day 7 after treatment with tea, separate sets of mice were given single doses of potassium dichromate and sodium arsenite, then killed after 24 h. Control sets were treated with potassium dichromate or sodium arsenite separately and also observed after 24 hours. The concentration of each salt corresponded to 1/10th of its LD50 value. Chromosomes were studied from bone marrow cells following the usual colchicine-hypotonic-fixation-air-drying Giemsa schedule. Both metallic salts were highly clastogenic when given alone, inducing a high frequency of chromosomal aberrations as compared with distilled water. Tea alone, given twice daily for 6 days, was not clastogenic. When mice, given tea twice daily for previous 6 days, were treated with either of the two salts on day 7, the degree of chromosome damage induced was reduced significantly as compared with the salts given alone. This reduction was more significant for sodium arsenite as compared with potassium dichromate. Such protection against arsenic cytotoxicity by prolonged dietary administration of black tea infusion is of importance in view of the widespread exposure of human population to arsenic damage through drinking water from tubewells in West Bengal, India and adjoining Bangladesh.