Turmeric and its main constituent curcumin were assessed in vivo for their anticlastogenic potential. In one experimental set, Swiss albino male mice were given turmeric (8, 12 and 16 mg/kg body weight) or curcumin (2, 4 and 8 mg/kg body weight) as a single intraperitoneal injection. In another set, the mice were given 8 mg/kg body weight of turmeric or one of three concentrations of curcumin (2, 4 and 8 mg/kg body weight) as a dietary supplement by gavage for 7 consecutive days. 30 min after the last dose the mice were administered a single acute dose of two known clastogens, cyclophosphamide (CP) (20 mg/kg body weight) or mitomycin C (MMC) (1.5 mg/kg body weight). After 18 hr, chromosome preparations were made from bone marrow cells. The endpoints studied were chromosome aberrations and damaged cells. Clastogenicity of the chemicals was compared using turmeric- or curcumin-primed and non-primed animals. As single agents turmeric and curcumin were not clastogenic even after 7 days of priming. Turmeric/curcumin could not inhibit CP- or MMC-induced clastogenicity. Although curcumin is reported to be the active chemopreventive principle in turmeric effective against a number of potential carcinogens in several experimental systems, it was virtually ineffective against the clastogenicity of CP or MMC at the doses tested.