Experiments were conducted with domestic swine in an attempt to accelerate and/or modify spontaneous or cholesterol-induced atherosclerosis through immune complex-produced changes in the arterial wall. For the purpose of comparison, another experiment was carried out with rabbits. Swine differed completely from rabbits in that various experimental designs failed to produce immune complex arteritis and fibroproliferative arteriosclerosis. In addition, two foreign serum infusions (human plasma and horse serum on the 30th and 60th day, respectively, 350 mg/kg foreign protein/infusion/animal) did not produce a significant effect on spontaneous arteriosclerosis and cholesterol-induced atherosclerosis (4 months atherogenic diet) in the arterial system of swine. In the aortic trifurcation, however, it was found that antigen administration slightly enhanced cholesterol-dependent atherogenesis.