Heparin was isolated from the whole carcass and skin of rats of the Wistar strain and crystallized as the barium salt. The sodium salt derived from this had a specific anticoagulant activity (Howell assay) of 47.5 International Units/mg and specific metachromatic activity of 101.5 International Units/mg. Yield of heparin was 0.55 mg/100 g body weight.