A multifactorial model for demonstrating the pathogenesis of the diet-induced atheromatosis of the rabbit is described. We examined the effect of various diets (atherogenetic, rich in fibre, mixed, normal) and of extreme restriction of movement, with and without doses of acetylsalicylic acid. The aorta showed uniforms morphological findings; 1. Acetylsalicilic acid no influence on the cholesterol-induced atheromatosis of the rabbit; 2. An atherogenic diet and a diet rich in raw fibre caused different degrees of sclerosis of the aorta; this was related to the cholesterol content of the mixed diet, which was 50% less than the cholesterol content of the atherogenic diet; 3. Macro- and microscopic examination showed that extreme restriction of movement alone has no demonstrable effect on the aorta of the rabbit; 4. The cholesterol-induced atheromatosis showed significantly less involvement of the aorta when there was extreme restriction of movement in addition to the diet; 5. In none of the test groups could we demonstrate any effect of PAT I on platelet adhesiveness; 6. The test conditions did not result in an activation of the contact phase of the haemocoagulation system.