1. Effects of various drugs on cholesterol-induced atherosclerosis in rabbits during the progression phase have been studied. The drugs tested are antimetabolites (mercaptopurine, hydroxyurea), surface active agents (sodiumdodecyl sulfate), inhibitor of adrenocoritcal steroid synthesis (o, p'-DDD), lysosome stablizers (chloroquine, acetylsalicylic acid) with antihistaminic (chlorpheniramine) and cholesterol binder (nystatin). 2. Mercaptopurine treatment showed marekd reduction in both atherosclerotic lesions and cholesterol concentrations of the serum and aorta. 3. Hydroxyurea reduced both the aortic cholesterol concentration and the lesions, but the serum cholesterol concentration remained high. 4. Sodiumdodecyl sulfate and o, o'-DDD showed slight inhibition of the development of atherosclerosis. 5. Pyridinocarbamate showed a slight beneficial effect on the prevention of atherosclerosis only when it was administered prior to the meal. 6. Nystatin, chloroquine and acetylsalicylic acid + chlorpheniramine showed little effect.