In a 10 year prospective study, we investigated the utility of the level of serum gamma-glutamyl transferase (GGT), a biological marker of alcohol consumption, in predicting the development of hypertension in Japanese male drinkers, all of whom lived in a rural community. The study included 77 men, aged 30-69 years, who were normotensive (SBP < or = 140 mmHg and DBP < or = 90 mmHg) and who had no prior history of antihypertensive treatment at baseline (1979-80). Hypertension was defined as SBP of > 140 mmHg and/or DBP of > 90 mmHg and/or starting antihypertensive medication. The age-adjusted relative risk for subjects with a serum GGT level of 20 U/l or higher compared with those with a level of < 10 U/l was 4.18 (95% confidence interval, 1.59-11.01, P = 0.004). The relative risk remained significant after adjustment for baseline BP level and the amount of alcohol consumption. These results suggest that the serum GGT levels may predict the future development of hypertension among drinkers.