The applicability of Cohn's method number 10 to the study of dog plasma has made possible this investigation of experimental canine atherosclerosis. Administration of thiouracil which causes hypercholesterolemia but no atherosclerosis in dogs produces no considerable alteration in the distribution of plasma lipoproteins. High cholesterol feeding and administration of thiouracil causes both atherosclerosis and significant alterations in the distribution of lipoproteins.