Studies have indicated that systolic (SBP) and diastolic (DBP) blood pressure are multi-factorial traits and significantly heritable. The aims of the present study are to assess whether the glutathione S-transferase M1 (GSTM1) and T1 (GSTT1) genotypes are associated with SBP and DBP of normotensive subjects and to ascertain whether the level of SBP and DBP given exposure to cigarette smoking is modified by the specific genetic polymorphisms of GSTM1 and GSTT1 This cross-sectional study was conducted on 140 subjects (49 females and 91 males) (mean age +/- SD: 38.7 +/- 14.7). The genotypes were determined using a polymerase chain reaction based method. Individuals were stratified according to the mean values of DBP and SBP, lower than or maximally same as the mean value defines as group I and higher than the mean value defines as group II. The logistic regression analyses were used. The best models fitted by logistic regression analysis for variables were associated with SBP and DBP. For analysis the combination of genotypes, sex, and smoking behaviour was used as qualitative variables, and age, body mass index (BMI), and heart rate were used as covariates. Combination of "present-GSTT1, null-GSTM1" genotype (OR = 0.001, 95% CI = 0.00-0.439 P = 0.025), heart rate (OR = 1.065, 95% CI = 1.018-1.114, P = 0.006), and interaction between BM I and combination of "present-GSTT1, null-GSTM1" (OR = 1.319, 95% CI = 1.058-1.644, P = 0.014) was associated with SBP. There was no association between either combination genotypes of GSTs or interaction of genotypes and smoking behaviour on DBP. The present results suggest that the GSTM1 gene is one of the candidate genes that alter the baseline of SBP in normotensive individuals. (C) 2004 Elsevier Inc. All rights reserved.