Beta-glucans are water-soluble cell-wall polysaccharides consisting of (1-->3,1-->4)-linked beta-D-glucopyranosyl monomers that comprise a considerable proportion of soluble fiber from certain grains including oats and barley. Consumption of foods containing beta-glucan or beta-glucan-enriched fractions prepared from these grains lower serum cholesterol concentrations in humans and in animal models of hypercholesterolemia. The present study was conducted to evaluate the toxicity of beta-glucan-enriched soluble fiber from barley in Wistar rats on dietary administration at concentrations of 0.7, 3.5 and 7% beta-glucan for 28 days. There were no adverse effects on general condition and behavior, growth, feed and water consumption, feed conversion efficiency, red blood cell and clotting potential parameters, clinical chemistry values, and organ weights. Necropsy and histopathology findings revealed no treatment-related changes in any organ evaluated. A dose-dependent increase in full and empty cecum weight was observed. This is a common physiological response of rodents to high amounts of poorly digestible, fermentable carbohydrates, and was of no toxicological concern. The only finding of possible biological relevance was an increase in the number of circulating lymphocytes observed in males. However, the increase was not dose-dependent and was not observed in females. Results of this study demonstrated that consumption of concentrated barley beta-glucan was not associated with any obvious signs of toxicity in Wistar rats even following consumption of large quantities.