Atheroma is still the major cause of mortality in the Western world, and the difference in prevalence of atheroma in developed and developing countries has caused speculation that absence of a dietary constituent may play a major aetiological part in the production of arterial disease. Interest has recently centred on the possible role of dietary fibre intake in the pathogenesis of atheroma. Bran reduces the bacterial degradation of bile salts in the colon and may increase colonic transit times, though these results are difficult to interpret because of the variability of these values. Several workers have suggested that dietary roughage may play a significant part in lipid metabolism. Moore has shown that atheromatous degeneration in rabbits that were fed an atherogenic diet was reduced by the presence of dietary roughage. Recently Heaton and Pomare showed a significant lowering of serum triglycerides and plasma calcium levels in both normal volunteers and patients with gall bladder disease when unprocessed wheat bran was added to their diet. Connell et al., however, failed to show any effect of bran on cholesterol or triglyceride levels in a group of normal medical students. The exact place of bran in the management of lipid disorders is therefore uncertain. In the light of these conflicting reports and because raised triglyceride levels are a significant risk factor in the genesis of atheroma we thought it important to clarify the problem by studying the effect of wheat bran on raised triglyceride levels in patients with primary type IV hyperlipoproteinaemia.