The aim of this study was to determine the association between coding variants in the human tissue kallikrein 1 (KLK1) gene and baseline blood pressure (BP) and antihypertensive response to irbesartan treatment in Chinese hypertensive patients. A total of 1061 hypertensives were recruited and received daily oral dosage of 150 mg irbesartan for 4 weeks. Predose BPs, BPs and blood irbesartan concentrations at postdose on the 28th day were all measured. Common functional singlenucleotide polymorphisms (SNPs) in the KLK1 gene were genotyped. On the basis of the HapMap data of Han Chinese in the Beijing population, two non-synonymous polymorphisms with minor allele frequency40.1, SNP rs5517 (Glu162Lys) and rs5516 (Gln121Glu), were selected. Those with GG genotype in the rs5516 locus had higher average baseline systolic BP (SBP) than CC subjects (b±s.e.: 5.0±2.3, P ¼ 0.033); and no associations of rs5517 with baseline BP (diastolic BP (DBP) and SBP) and BP responses, or rs5516 with baseline DBP and BP response were observed. In a haplotype-based association test for the KLK1 gene, the Haplo-special score analyses identified that haplotype AG was marginally associated with SBP response (specific score: 1.75 for P ¼ 0.08), but not with DBP response. We did not find any associations between haplotypes (GC and AC) and BP responses. The Haplo-GLM analyses showed that, compared with haplotype GC subjects, the subjects with haplotype AG had a marginally greater SBP response (adjusted b ± s.e.: 1.81 ± 0.97, P ¼ 0.06), but DBP response did not differ. This study suggests that rs5516 in the KLK1 gene may be involved in the development of essential hypertension and in the regulation of SBP-lowering response to irbesartan in Chinese hypertensives.