This study investigates the mechanisms of action for the hypocholesterolaemic effects of sugar-beet fibre (SBF) and guar gum. Four groups of ten male Wistar rats were fed ad lib. on test diets containing either 100 g SBF or guar/kg, or control diets containing 100 g cellulose or wheat bran/kg for 28 d. Food intake, weight gain and food consumption ratios were unaffected by the diets. Circulating cholesterol and hepatic cholesterol concentrations were significantly lower in both SBF- and guar-fed groups compared with either cellulose- or bran-fed animals. Circulating triacylglycerol concentrations were significantly lower in SBF- and guar-fed animals, but total hepatic lipid concentrations and hepatic and adipose tissue lipogenesis rates were unaffected by the diets. Hepatic cholesterol-7 alpha-hydroxylase (EC 1.14.13.17) activities were significantly higher in the guar-fed animals compared with cellulose or bran control groups. Hepatic 3-hydroxy-3-methylglutaryl-CoA reductase (EC 1.1.1.88) activities were unaffected. Circulating bile acid concentrations were significantly lower in SBF- and guar-fed animals and faecal bile acid output was significantly higher in the guar-fed group compared with bran- or cellulose-fed groups. This study supports the hypothesis that guar exerts its hypocholesterolaemic effect via intraluminal bile acid binding and loss of cholesterol from increased faecal bile acid excretion. The mechanism of action for the hypocholesterolaemic effect of SBF is less clear; the results of the present study point to a mechanism involving disruption of the enterohepatic bile acid circulation, possibly via changes in the rate of absorption of dietary lipid.