Most placebo-controlled studies testing the hypo-cholesterolaemic action of oat bran have compared high fibre against low fibre diets. To determine whether oat bran had greater cholesterol-lowering action than another source of fibre (wheat bran) we compared the effect of breads of similar total fibre content containing either oat bran or additional wheat bran. Twelve hyperlipidaemic subjects (38-66 years) were stabilised on lipid-lowering diets for at least three months prior to the study. Subjects were given each type of bread for four-week periods in a single-blind, cross-over design. Cholesterol, triglyceride and LDL-cholesterol levels did not change significantly during the oat and wheat bread periods. HDL-cholesterol rose equivalently but only to a just significant level during the oat bran diet. Body weights, lipids and lipoprotein parameters were not significantly different between the two diet periods. Both diet treatments lowered serum cholesterol approximately 4%. We conclude that this oat bran bread consumed as part of a lipid-correcting diet did not influence lipoproteins to any greater extent than wheat bread of similar total fibre content.