The effects of the addition of 15% or 30% non-heated oat bran or 30% baked oat bran to a purified diet on apparent digestibility of dry matter, protein, lipid and fiber were measured in balance experiments with male Wistar rats. The effects of oat bran on dietary metabolizable energy, fecal bulking capacity and transit time of the ingested food were also studied. Heat processing of oat bran occurred in conditions of moisture and temperature similar to those of bread baking. Compared with the unprocessed oat bran, the baked product had a higher content of insoluble fiber, mainly due to higher Klason lignin content and a shift from soluble to insoluble beta-glucans. Relative to the fiber-free control diet, feeding the oat bran diets increased wet and dry fecal weight and decreased the transit time of the food. Fecal bulking capacity increased proportionally with oat fiber intake. Metabolizable energy of the diets, as well as apparent digestibility of dry matter and protein decreased with oat bran supplementation; on the other hand, lipid digestibility was not significantly changed. Baking of oat brain resulted in no statistically significant effects on dietary metabolizable energy or apparent digestibility of dry matter, protein, lipid and fiber. The measured metabolizable energy of oat bran ranged between 12.7 and 13.2 MJ/kg. Total plasma cholesterol concentration diminished with oat brain intake; non-heated and baked oat bran had comparable effects on plasma cholesterol. An inverse linear relationship (r = -0.80, P less than 0.1) was found between plasma cholesterol concentration and fecal excretion of bile acids.