Responses to the changes in dietary sodium and posture were investigated in 9 young clinically healthy Japanese males who customarily consumed a larger amount of salt than North Americans or Europeans of mixed white ethnic background. Plasma renin activity (PRA), plasma aldosterone concentration (PAC), and urinary aldosterone excretion rate (AER) differed at each end of 3- to 4-day spans on a "control", a high-salt and a low-salt diet and of furosemide administration. PRA and PAC, also determined during the upright position following the supine blood sampling, increased after only 1 hour of standing in each condition (p<0.05 or more). PRA and PAC were well correlated in all 4 conditions, regardless of the posture (r=0.806, p<0.001). There were also highly significant correlations between the "supine" PRA or PAC and the preceding 24-hour AER (r=0.869, p<0.001 for PRA; r=0.855, p<0.001 for PAC). Correlation coefficients between PRA and PAC in 9 individual subjects ranged from 0.823 to 0.987. The estimates of constant and slope of the regression line between PRA and PAC varied from subject to subject. The renin-aldosterone axis in response to changes in dietary sodium and posture must be individually assessed