The present study investigated whether a combined treatment of niacin and chromium (III) chloride caused a protective effect on the intestine of hyperlipidemic rats. Rats were divided into four groups: (I) rats were fed with pellet chow, (II) with a lipogenic diet for 60 days, (III) with a lipogenic diet and treated with 100 mg/kg niacin and 250 mu g/kg chromium chloride for 45 days by the gavage technique after experimental animals had became hyperlipidemic (15 days), and (IV) with pellet chow and treated with the same dose of niacin and chromium chloride for the last 45 days. Hyperlipidemic rats displayed a reduction of the intestinal glutathione level and an increase in intestinal lipid peroxidation levels, and in serum cholesterol, total lipid and phospholipids levels. However, treatment with niacin and chromium reversed the effect of hyperlipidemia. Light microscopy revealed compressed villi, oedema, mononuclear cell filtration, and vacuolization on the cytoplasm of epithelial cells in the jejunum of hyperlipidemic rats. Ultrastructurally, the disruption of arrays of rough endoplasmic reticulum cisternae, an increase and gathering in smooth endoplasmic reticulum, swelling in mitochondrial cristae and lipid vacuoles were detected in epithelial cells of hyperlipidemic rat jejunum. Despite individual differences, degenerative findings were decreased in hyperlipidemic rats given niacin and chromium. Niacin and chromium treatments had a protective effect on the intestine of the hyperlipidemic rats as well as a lipid-reducing effect.