The individual effects of dietary cholesterol and fat saturation on plasma lipoprotein concentrations were determined in an ethnically diverse population of normolipidemic young men (52 Caucasian, 32 non-Caucasian). The experimental diets contained approximately 200 or 600 mg/d of cholesterol, 36-38% of calories as fat, and high or low proportions of saturated and polyunsaturated fat (polyunsaturated/saturated fat ratio approximately 0.8 vs 0.3). At the lower cholesterol intake, the high saturated fat diet had only a modest effect on LDL cholesterol in Caucasians (+ 6 mg/dl-1) and none in non-Caucasians. 600 mg cholesterol with high saturated fat led to a substantial mean increase in LDL cholesterol, which was significantly greater in Caucasian than in non-Caucasian subjects (+ 31 mg/dl vs 16 mg/dl, P < 0.005). 600 mg cholesterol with increased polyunsaturated fat gave a mean LDL increase of 16 mg/dl, lower than found when the same high cholesterol intake was coupled with increased saturated fat. Variation in cholesterol rather than the proportions of saturated and polyunsaturated fat had the most influence on LDL-cholesterol levels. Among non-Caucasians it was the only significant factor.