It is known that moderation of alcohol intake reduces blood pressure, although the exact mechanism has not yet been established. To clarify the hypotensive mechanism of alcohol reduction, we evaluated the change in cellular magnesium and sodium metabolism during alcohol reduction in mild hypertensive patients. We measured intraerythrocyte sodium and magnesium, intraplatelet free magnesium concentrations, and erythrocyte ouabain-sensitive 22Na efflux rate constant (Kos) in 17 mild essential hypertensive patients regularly consuming more than 40 g/day of alcohol, before and after 4 weeks of alcohol reduction, and 12 age-matched nondrinking hypertensives. Intraerythrocyte magnesium (P < .01) and intraplatelet free magnesium (P < .05) concentrations were significantly lower in drinkers than in nondrinkers. In drinkers, advice to reduce alcohol intake for 4 weeks resulted in a reduction in self-reported alcohol consumption from 461.7 to 71.6 g/week, a significant fall in both supine systolic blood pressure (136.3 +/- 10.8 to 130.8 +/- 11.3 mm Hg, P < .001) and supine diastolic blood pressure (85.1 +/- 8.6 to 82.6 +/- 8.7 mm Hg, P < .05). The fall in mean blood pressure correlated positively with the reduction in weekly alcohol consumption. Intraerythrocyte magnesium and Kos were increased (P < .05, P < .01, respectively), while intraerythrocyte sodium was decreased (P < .01). The increase in intraerythrocyte magnesium correlated negatively with the fall in mean blood pressure and positively with the increase in Kos, which correlated negatively with the decrease in intraerythrocyte sodium.(ABSTRACT TRUNCATED AT 250 WORDS)