The carcinogenic potential of tamarind seed polysaccharide was examined in both sexes of B6C3F1 mice. Groups of 50 male and 50 female animals were given diets containing 0, 1.25 and 5% of tamarind seed polysaccharide for 78 wk. Body weight retardation was exhibited by the females in the 1.25 and 5% groups from 34 wk to termination. However, there were no treatment-related clinical signs or adverse effects on survival rate, food and water consumption, haematology findings or organ weights. Detailed histopathological examination also revealed no treatment-related increase in the incidence of any non-neoplastic or neoplastic lesions. These results demonstrated that tamarind seed polysaccharide is not carcinogenic in B6C3F1 mice of either sex.