We tested the specificity of the plasma cholesterol-lowering effect of linoleic acid in a comparison of linoleate-rich and saturated fatty acid-rich foods. Twelve mildly hypercholesterolemic men and women ate the two diets for three weeks each in a random cross-over design, after a two-week baseline period. A linoleic acid-rich supplement was added to the baseline diet so that the saturated and monounsaturated fatty acid content did not change significantly. Despite the consequent increase in total fat intake, the linoleate-rich diet (23 per cent energy from polyunsaturated fatty acids) significantly lowered plasma total and low-density lipoprotein (LDL) cholesterol (-8 per cent and -14 per cent respectively), while high-density lipoprotein (HDL) cholesterol rose 8 per cent. The direction of these changes was similar in all 12 subjects. Compared with a supplement that raised dietary saturated fatty acids to 30 per cent energy, the linoleate acid-rich diet gave lower total cholesterol (-14 per cent), LDL cholesterol (-18 per cent) and HDL cholesterol (-12 per cent) concentrations. Linoleic acid lowers LDL cholesterol even when saturated fatty acids are not significantly displaced and substantially more when there is such displacement.