Large-scale genome-wide association studies (GWASs) have identified significant associations of common genetic variants with blood pressure (BP) levels. To obtain more evidence for the role of these variants in BP regulation, we studied their association with BP responses to four different antihypertensive drug monotherapies. We selected 19 single-nucleotide variants based on data from five GWASs. The study group consisted of more than 200 hypertensive Finnish men from the GENRES study. Ambulatory BP responses to 4-week treatments with losartan, bisoprolol, hydrochlorothiazide and amlodipine were the primary targets of the study. Secondarily, baseline indicators of the activity of the renin-angiotensin-aldosterone system were studied. After correction for multiple comparisons, the variant rs6749447 in the STK39 gene was significantly associated with BP responses. Thus, the minor rs6749447 allele was associated with a lower systolic and diastolic BP response to losartan (P=0.0005 and 0.0002, respectively). rs6749447 minor allele homozygotes had marginally higher serum aldosterone/plasma renin activity (PRA) ratios (P=0.04) than those without this allele. In a replication study on aldosterone and renin levels, another cohort of hypertensive patients (n=311) showed a similar trend. When the two cohorts were combined, the aldosterone level (P=0.02) and the aldosterone/PRA ratio (P=0.01) were higher in subjects homozygous for the minor rs6749447 allele than in other subjects. The present study shows that pharmacogenetic approaches may provide evidence that complements systematic genome-wide strategies by identifying gene loci that not only affect the BP level but also might modify its response to pharmacologic interventions.