Objective: To investigate the lipid-lowering potential of a butter-fat modified through manipulations in bovine feeding to increase the unsaturated : saturated fatty acid ratio. Design: Double-blind, randomised, cross-over intervention trial. Setting: University of Auckland Human Nutrition Unit, New Zealand. Subjects: Twenty healthy, male subjects. Intervention: A residential trial in which all foods and beverages were provided during two intervention periods, comprising 3 weeks of high unsaturated 'modified' vs 3 weeks of saturated 'control' butter feeding separated by a 4 week washout. Diets were of typical composition of 39 percentage energy (en%) fat (20 en% butter-fat), 48 en% CHO, 13 en% protein.Results: There was a significant decrease in both total (P < 0.05, 7 7.9%) and LDL-cholesterol (P < 0.01, 7 9.5%) during modified butter feeding. There was no significant effect of treatment on a range of other risk factors including HDL-cholesterol, triglyceride, apolipoprotein A or B, nonesterified fatty acids (NEFA), haemostatic clotting factor VII and fibrinogen or glucose (P > 0.05). Subjects were maintained in energy balance and there was no significant change in body weight during intervention. Butter-fat composition alone differed between treatments. Conclusions: A significant improvement in cardiovascular risk can be achieved by moderate changes in dietary fatty acid profile, achieved through a common and well accepted food source, butter-fat. Sponsorship: New Zealand Dairy Board, Wellington;