To investigate the association of CYP1A2 genetic polymorphisms with the inducing effect of heavy coffee consumption on CYP1A2 activity in Serbian and Swedish populations, and to determine the frequency of the CYP1A2 genetic polymorphisms in Serbs.Using PCR-RFLP and the tag-array minisequencing method, 126 Serbian healthy volunteers were genotyped for -3860G>A, -2467delT, -739T>G, -729C>T, -163C>A, 2159G>A, and 4795G>A. For 64 nonsmoking participants, the data on CYP1A2 activity (plasma paraxanthine/caffeine ratio) and coffee consumption habit were available from our previous study. The data on CYP1A2 genotype, enzyme activity, and coffee consumption from 114 Swedish healthy nonsmoking subjects were included in the analyses.In Serbs, CYP1A2 polymorphisms -3860G>A, -2467delT, -739T>G, -729C>T, -163C>A, and 2159G>A were found at the frequencies of 0.4, 5.0, 3.4, 0.7, 61.1, and 56.0%, respectively, while 4795G>A was not detected. Significant association of heavy coffee consumption with high CYP1A2 enzyme activity was observed only in carriers of -163 A/A. Increasing effect of -163C>A on CYP1A2 inducibility was found in both Serbian (P=0.022) and Swedish (P=0.016) nonsmoking heavy coffee consumers. There was no significant difference in CYP1A2 enzyme activity among genotypes in non-heavy coffee consumers. The results indicate that 22 and 14% of the phenotypic variability among Serbian and Swedish heavy coffee consumers, respectively, might be explained by -163C>A polymorphism.CYP1A2 polymorphism -163C>A has an important increasing effect on CYP1A2 inducibility by heavy coffee consumption and may possibly be a contributing factor for interindividual variations in CYP1A2 enzyme activity.