The anticlastogenic activities of a crude extract of leaves of spinach‐beet (Beta vulgaris var. benghalensis Hort.) and equivalent amounts of chlorophyll extracted from the leaves and of synthetic chlorophyllin in reducing cytotoxicity were compared following exposure of mice in vivo to a known clastogen chromium (VI) oxide. Male Swiss albino mice were administered orally the vegetable extract for 7 consecutive days and then exposed to the clastogen by gavage (20 mg/kg b wt). For comparison, equivalent amounts of extracted chlorophyll and synthetic chlorophyllin were administered to the mice, 2 h before exposure to the same dose of the metal. Chromosomes were studied from bone marrow cells 24 h after exposure, following colchicine‐hypotonic‐fixative‐flame drying‐Giemsa staining schedule. Chlorophyllin and the crude extract, when given alone, did not induce chromosomal aberrations and reduced the clastogenic effects induced by chromium (VI) oxide to a statistically significant level, indicating a protective action. Chlorophyll, however, produced a significant increase of chromosomal aberrations compared with control, when administered alone and was not able to reduce the clastogenicity of the metallic salt to a significant level. Copyright © 1995 John Wiley & Sons, Ltd.