To study dietary fat and cholesterol effects on plasma high density lipoprotein (HDL) metabolism and rates of apolipoprotein (apo) A-I catabolism, guinea pigs were fed 15% (wt/wt) lard- or corn oil-based diets with 0.01% (basal), 0.08%, 0.17% or 0.33% cholesterol. Absorbed dietary cholesterol provided 6%, 50%, 100% and 200%, respectively, of the daily endogenous cholesterol synthetic mass. While total plasma cholesterol concentrations increased significantly above basal levels at the 0.17% and 0.33% cholesterol intakes, plasma apo E-free HDL (EoHDL) cholesterol concentrations did not increase significantly until the 0.33% cholesterol level (P < 0.001). Fractional catabolic rates (FCR) of injected [131I]-apo A-I were not altered by dietary treatment, either fat saturation or cholesterol, but were inversely correlated with plasma EoHDL cholesterol levels (r = -0.622), suggestive of a regulatory role of turnover rates on HDL cholesterol levels independent of dietary treatment. Analysis of the high affinity EoHDL binding to isolated hepatic membranes suggested that hepatic binding was not a determinant of HDL catabolism, as dietary cholesterol-induced decreases in Bmax (binding capacity) were not correlated with changes in apo A-I FCR. Even though dietary cholesterol was associated with increased plasma EoHDL cholesterol and with decreased HDL binding protein Bmax, these values did not correlate with each other nor with effects on apo A-I FCR.