A crude extract of leaves of Indian spinach (Beta vulgaris L. var. benghalensis Hort.) was observed to modify significantly the cytotoxic effects of a known carcinogen, lead subacetate in mice in vivo, Laboratory bred male Swiss albino mice were fed by gavaging the crude extract for 7 days daily (1.5 g fresh weight of leaf per kg b.w. of animal). On day 7, mice were injected intraperitoneally with three concentrations of the carcinogen (20, 30, 50 mg/kg b.w.). Chromosomes were studied from bone marrow cells, 24 h after exposure, following colchicine-fixative-air drying-Giemsa schedule, The endopints screened were chromosomal aberrations (CA) and damaged cells (DC), Lead subacetate, given alone, induced both CA and DC in frequencies directly related to the concentration, The leaf extract given alone, did not induce any aberrations. Prior priming with the extract as a dietary supplement reduced significantly the cytotoxic effects of the two lower concentrations of the carcinogen.