The analysis of tin in biological materials is rarely reported. In this study, instrumental neutron activation analysis was used to determine the tin together with some other trace elements in various organs of rats treated with trialkyltin-methacrylic copolymer. No appreciable accumulation of tin and variation of distribution of trace elements (Cr, Fe, Zn and Co) in various organs are found. The pathological changes in the liver sections cannot be observed either. This therefore indicates that the toxicity of trialkyltin-methacrylic copolymer is low, if any.