The purpose of this study was to determine if there was a relationship between plasma beta-VLDL concentrations and atherosclerosis severity in cholesterol-fed pigeons, and if so, whether this correlated with cholesterol accumulation in tissues rich in cells of the monocyte-macrophage system (liver, spleen, peritoneal macrophages). Among individual birds consuming a cholesterol-containing diet, plasma beta-VLDL concentrations ranged from 14 to 1979 mg/dl. In these animals the cholesterol content of peritoneal macrophages, liver, and spleen was positively correlated with plasma concentrations of beta-VLDL and LDL, but not with HDL. When added in vitro to peritoneal macrophages from control pigeons, beta-VLDL stimulated a nearly 200-fold increase in cholesterol accumulation, but there was no relationship between the ability of beta-VLDL to stimulate macrophage cholesterol accumulation and the extent of atherosclerosis in the animal from which the beta-VLDL was obtained. Cholesterol feeding for up to 6 months increased the severity of atherosclerosis in both atherosclerosis-susceptible White Carneau and resistant Show Racer pigeons, but there was no correlation of atherosclerosis severity with beta-VLDL or HDL concentrations, and only a weak relationship with LDL concentrations. The results are consistent with the conclusion that atherosclerosis susceptibility in pigeons cannot be explained by quantitative or qualitative differences in plasma beta-VLDL. Instead, differences in susceptibility are probably mediated at the level of the arterial wall, perhaps by genetic differences that influence the way an individual animals' arterial cells (endothelial, smooth muscle, macrophages) interact with specific plasma lipoproteins.