The possibility that cycloartenol magnifies the hypocholesterolemic effect of beta-sitosterol was studied in two strains of rats fed on cholesterol-enriched (0.5%) diets. Cycloartenol was added to diets containing 1.0% or 0.5% beta-sitosterol at the 0.05% level and to diet free of plant sterol at the 0.5% level. In one experiment, diets included sodium cholate (0.125%). Due to the potent hypocholesterolemic efficacy of beta-sitosterol under the present dietary regimens, no clear additional effect (so-called synergistic effect) of cycloartenol was observed. However, in the experiment using Wistar rats, the decrease in serum apo A-I due to feeding cholesterol was ameliorated more effectively in combination with beta-sitosterol than with beta-sitosterol alone. The hepatic deposition of cholesterol was mitigated by dietary beta-sitosterol, and further, although slightly, by a combination of beta-sitosterol and cycloartenol, except in the experiment with diets containing sodium cholate. Fecal excretion of neutral and acidic steroids was not meaningly magnified by cycloartenol. Cycloartenol itself was not as effective as beta-sitosterol in mitigating lipid disorders due to dietary cholesterol. The rate of appearance of cholesterol in the thoracic duct lymph was not interfered with further by a combination of beta-sitosterol and cycloartenol compared to beta-sitosterol alone. This trimethylsterol was absorbed at a rate approximately 4-fold higher than that of beta-sitosterol, though much lower compared to cholesterol. These results suggest a preference for cycloartenol in cholesterol dynamics. However, cycloartenol seems unlikely to influence cholesterol absorption in the small intestine.