The response of serum lipids to dietary interventions varies considerably among individuals. Variations in genes important in the cholesterol metabolism could be important determinants for these interindividual differences. The rate-limiting enzyme in the conversion of cholesterol into bile acids is cholesterol 7alpha-hydroxylase (CYP7A1). An A to C substitution 278 bp upstream in the promoter of the CYP7A1 gene has been found. We investigated the effect of this polymorphism on responses of serum lipids to an increased intake in dietary cholesterol, cafestol, saturated fat and trans fat in 496 normolipidemic subjects. Adjusted for the apoE genotype effect, subjects homozygous for the A allele had a significantly lower response (0.00±0.02 mmol/1) of serum HI)L-cholesterol to a diet rich in cholesterol than CC carriers (0.17±0.04; p<0.001). In addition, AA carriers tended to have a lower response of serum total cholesterol (0.27±0.07) as compared to CC carriers (0.44±0.15; p-0.075). Upon intake of cafestol, AA carriers had a lower response of serum total cholesterol (0.69±0.10) than homozygous C carriers (1.01±0.10; p-0.028). AA carriers also tended to have a decreased response of apoB-containing lipoproteins (0.78±0.10) as compared to CC carriers (1.03±0.10; p-0.069). As expected, we did not find an effect of the CYP7A1 genotype on the response of serum lipids to an increase in dietary saturated and trans fatty acids. In conclusion, the CYP7A1 polymorphism has a considerable effect on the response of serum cholesterol after an increase in dietary cholesterol and cafestol, with a lower response in subjects homozygous for the A allele.