Many recent case-control studies have suggested a significant relationship between M235T (the substitution of threonine for methionine at position 235 codon) polymorphism of the angiotensinogen (AGT) gene and hypertension. To investigate whether the M235T polymorphism of AGT gene affects the incidence of hypertension, a retrospective cohort study was performed among Japanese workers. The subjects were Japanese workers at an occupational site in Shimane Prefecture in Japan. The baseline data were set at the received regular health examination in 1992, and a retrospective cohort study was performed for analyzing the incidence of hypertension in 1998. The rates of M235M (MM), M235T (MT) and T235T (TT) genotypes were 4%, 32% and 64%, respectively. The relative risks of MT and TT against MM for the incidence of hypertension by single variance analysis were 1.47 [95% confidence interval (CI) 0.50 - 4.33] and 1.35 (95% CI 0.47 - 3.90), respectively. The relative risks of MT and TT against MM for the incidence of hypertension, adjusted for sex, age, body mass index, fasting glucose and cigarette smoking, drinking and exercise in 1992, were 1.49 (95% CI 0.49 - 4.53) and 1.25 (95% CI 0.42 3.74), respectively. The data from this study suggest that the M235T polymorphism of AGT gene has a weak role in the manifestation of hypertension. Further comprehensive studies are needed to resolve this issue.