Objective: To determine whether substituting carbohydrate for saturated fat has any adverse effects on serum high density lipoprotein (HDL) cholesterol and triglycerides in free-living individuals. Design: Randomised crossover trial. Setting: General community. Subjects: Volunteer sample of 38 healthy free-living men with mean (s.d.) age 37 (7) y, moderately elevated serum total cholesterol 5.51 (0.93) mmolal and body mass index 26.0 (3.6) kgam 2 . Interventions: Participants completed two six week experimental periods during which they consumed either a traditional Western diet (36%, 18%, and 43% energy from total, saturated, and carbohydrate, respectively) or a low-saturated fat high-carbohydrate diet (22%, 6% and 59% energy from total, saturated, and carbohydrate, respectively). Dietary principles were reinforced regularly, but food choices were self-selected during each experimental period. Main outcome measures: Serum lipids, body weight and plasma fatty acids. Results: Reported energy and nutrient intakes, plasma fatty acids, and a drop in weight from 79.1 (12.5) kg on the Western diet to 77.6 (12.0) kg on the high-carbohydrate diet (P`0.001) con®rmed a high level of compliance with experimental diets. Total and low density lipoprotein (LDL) cholesterol fell from 5.52 (1.04) mmolal and 3.64 (0.88) mmolal, respectively on the Western diet to 4.76 (1.10) mmolal and 2.97 (0.94) mmolal on the high-carbohydrate diet (P`0.001). HDL cholesterol fell from 1.21 (0.27) mmolal on the Western diet to 1.07 (0.23) mmolal on the high-carbohydrate diet (P 0.057), but the LDL:HDL cholesterol ratio improved from 3.17 (1.05) on the Western diet to 2.88 (0.97) on the high-carbohydrate diet (P 0.004). Fasting triglyceride levels were unchanged throughout the study. Conclusions: Replacement of saturated fat with carbohydrate from grains, vegetables, legumes, and fruit reduces total and LDL cholesterol with only a minor effect on HDL cholesterol and triglyceride. It seems that when free living individuals change to a ®bre rich high-carbohydrate diet appropriate food choices lead to a modest weight reduction. This may explain why the marked elevation of triglyceride and reduction of HDL cholesterol observed on strictly controlled high-carbohydrate diets may not occur when such diets are followed in practice.