Sulphatide is found to be a major glycosphingolipid in serum lipoproteins of rabbit and its content is markedly elevated in serum of WHHL rabbit, an animal model for human familial hypercholesterolemia. On analysis of tissue sulphatide contents, serum appears to derive its sulphatide from liver (90%) and small intestine (10%) and passes on to aorta of WHHL rabbit which is found to have a large amount of sulphatide while none is found in normal aorta. Thus it seems that sulphatide finally accumulates in arterial walls along with the progression of atherosclerosis in WHHL rabbit. Since sulphatide at median concentration (8 nmole/ml serum) in various mammals is found to increase activated partial thromboplastin time by 25%, it is suggested that anticoagulant activity may be one of the physiological functions of sulphatide in serum. The observation of an increase in activated partial thromboplastin time by 2.5-fold on injection of sulphatide (10 mg/kg body wt) into rabbit suggests that sulphatide may be an effective and safe antithrombotic agent.