The use of heparin during intraven. infusions in some 50-60 cases was satisfactory, no cases of thrombosis resulted, there was no recurrence of hemorrhage in hemor- rhagic cases, no toxic or deleterious effects when the amt. of heparin was 1 unit/ml. When penicillin solns. were in-fused the conc. of heparin was raised to 3 units/ml. This amt. is sufficient to prevent thrombosis. In none of the cases was the clotting time of the blood of the patient altered significantly.