The effect of exogenous heparin on triton lipemia induced in rats was studied in 2 expts. 5×25 mg of Triton WR-1339 injected at intervals of 12 hrs caused an abrupt increase in the blood cholesterol and fat levels. They were both lowered distinctly by 50 IU of heparin injected concomitantly with triton. In the second experiment, 3×25 mg of triton provoked a smaller but significant elevation in the lipemia of rats. 3 × 250 IU of heparin nullified the hypercholesterinemia and the lipemia completely. Smaller doses of heparin caused a gradually diminishing inhibition of triton induced lipemia. The results of these two experiments and one of our earlier experiment suggest that Triton WR-1339 inhibits the release of heparin especially from the mucosal mast cells of gastrointestinal tract. Triton does not inhibit the activation of the clearing factor with exogenous heparin. Under these circumstances, it is possible to measure the shortage of endogenous heparin by replacing it with exogenous heparin using the level of lipemia as indicator.