Hypertensives screened among a work-site male population were treated either with or without antihypertensive drugs according to WHO stage of hypertension, and followed up by medical teams at the work site. The outcome during 8 years of follow-up was compared between two hypertension cohorts; one (cohort 1) instituted in 1970 included 1,092 hypertensives from 11,860 employees, while the other (cohort 2) made in 1975 contained 1,190 from 10,789 persons. Age-adjusted mortality or morbidity rate from cardiovascular diseases (CVD) was lower in cohort 2 than in cohort 1. Multiple regression analysis was used to adjust inter-cohort differences in factors to influence the prognosis, showed that CVD occurred less frequently in cohort 2 than in cohort 1. The results suggest that this system of controlling blood pressure is useful in preventing CVD in a large population.