1. Aqueous celery extract was administered intraperitoneally to genetically hypercholesterolaemic (RICO) and normocholesterolaemic (RAIF) rats via Alzet osmotic pumps over a 13 day period. 2. The serum cholesterol concentration of the celery extract-treated RICO rats was found to be significantly lower (P < 0.05) than the control rats. Aqueous celery extract was effective in preventing the rise of cholesterol level in the RICO rats. However, no such observation was seen in the RAIF rats. The serum triglyceride level was unchanged in both strains of rats. 3. When 3-n-butylphthalide (BuPh), a unique component in celery, was administered in the same manner to the RICO and RAIF rats, it did not produce significant changes in the serum and liver lipid profiles of these rats. The activities of hepatic 3-hydroxy-3-methylglutaryl CoA reductase in both strains of rats were also not significantly different from their respective controls. 4. Together with our recently reported thin-layer chromatography findings that BuPh was not detected in the aqueous celery extract, this study suggests that the effect of celery extract on serum cholesterol levels in the RICO rats could be attributed to chemical constituents other than BuPh.