A crude extract of Allium sativum (100 mg/kg b.w./day) was administered orally to Swiss albino mice with a normal diet for 30 days. Sodium arsenite, a known cytotoxic agent, was given subcutaneously in normal saline to mice (0.1 mg/kg b.w. == 1/50 of LD50) on days 7,14,21 AND 30 of experiments. Chromosomal studies were conducted on bone marrow preparations following the colchicine-air-drying Giemsa schedule. The frequency of chromosomal aberrations was significantly lower in animals maintained on crude plant extract as a dietary supplement during exposure to sodium arsenite as compared to those treated with arsenite alone. A crude extract of Allium sativum thus protects against the clastogenicity of sodium arsenite. © 1993 Informa UK Ltd All rights reserved: reproduction in whole or part not permitted.