The prolonged administration of either heparin or dicoumerol has been demonstrated to be effective in retarding the formation of atheromata in the cholesterol-fed chick. This beneficial action is possibly produced as a result of a demonstrated antihypercholesteremic action exerted by these anticoagulants.

Heparin is ineffective in preventing the marked turbidity of sera from cholesterol-fed chickens.

After the formation of atherosclerosis in the chick neither heparin nor dicoumerol is effective in hastening the regression of this condition. The serum lipid picture as well as the degree of atheroma of the various groups in the regression experiments is unaffected by the anticoagulants.