To augment the effectiveness of conventional lipid-lowering treatment, a diet has been evolved combining modified fat content with an increase in vegetable-derived fibre and protein. This was evaluated in 37 hyperlipidaemic and normal ambulant subjects in whom plasma lipid and lipoprotein responses were measured for 4.7-11 months. Mean reductions in plasma cholesterol, triglyceride and low density lipoprotein cholesterol levels were 22, 24 and 25% respectively; there was no significant change in the cholesterol concentrations in high density lipoprotein or in its HDL2 subclass. The effectiveness of the diet in reducing hyperlipidaemia, its influence in optimizing the distribution of cholesterol between plasma lipoprotein classes, and its nutrient composition suggest that it is an advance on existing lipid-lowering dietary patterns.