In the CYP3A5 gene, the A>G (*3) and G>A (*6) polymorphisms result in severely decreased expression of CYP3A5 enzyme relative to a normal functional allele (*1). We sought to determine if the CYP3A5 genetic polymorphisms were associated with level of blood pressure (BP), risk of hypertension (HTN), and the antihypertensive response to verapamil. A total of 676 normotensive and hypertensive participants (mean age 49+/-8.2 years) from the Hypertension Genes study and 722 patients (mean age 66+/-9 years) from the International Verapamil/Trandolapril Study Genetic Substudy (INVEST-GENES) were genotyped for CYP3A5 to test for associations with BP, HTN, and in the latter cohort, antihypertensive response to verapamil. CYP3A5 haplotypes were determined using PHASE 2, with any allele containing either (*3) or (*6) designated as non functional. In the HTN genes population, there were no significant differences based on the number of functional CYP3A5 alleles, in systolic blood pressure (SBP) or diastolic blood pressure (DBP) among the normotensive whites or blacks (all P> or =0.70) or in allele frequency between normotensives and hypertensives. In INVEST-GENES, when controlled for baseline BP, race, age, and gender, untreated BP in carriers versus non carriers of a CYP3A5 functional allele was 158.2+/-13.7 and 154.8+/-13.7 (P=0.061), respectively. CYP3A5 functional allele status was marginally associated with the SBP response to verapamil in blacks (P=0.075) and Hispanics (P=0.056), but not in whites (P=0.40), with the effect being largely driven by higher SBP in the carriers of two functional alleles. There was no association with DBP response and CYP3A5 allele status. CYP3A5 genotype does not contribute importantly to BP or risk of HTN, but may influence response to calcium channel blockers in populations in which carrier status of two functional alleles is common.