The effects of ingested oat and barley gums on plasma and liver lipid concentrations were examined in genetically obese and lean Zucker rats. Soluble gum preparations extracted from oat and barley were composed mainly of a nonstarchy glucan. Obese and lean male Zucker rats, aged 6 weeks, were fed a standard diet or diets containing gum preparations corresponding to 2% total dietary fiber for 34 days. Liver hypertrophy, fatty liver and hyperlipidemia were observed in obese rats fed a standard diet, compared with their lean littermates. Both oat and barley gums suppressed liver lipid accumulation and elevation of plasma cholesterol concentration in obese rats, whereas plasma triglyceride concentration in both gum groups was rather higher than that in the standard group. The influence of gums on plasma and liver lipid concentrations in lean rats was less marked than that in obese rats. These results indicate that ingested oat and barley gums ameliorate fatty liver and hypercholesterolemia in obese Zucker rats.