Blood pressures, pulse rates and 24-h urinary electrolyte content were measured in 371 male and 125 female randomly selected civil servants. The male and female subjects were divided into nine subgroups each, by tertiles of sodium (Na) excretion and tertiles of pulse rate. Those in the subgroup with highest values for both variables had the highest mean systolic and diastolic blood pressure (adjusted to age 50 years and a body mass index of 25 kg/m2) among the male and female groups, and those in the subgroup with lowest values for both variables had the lowest systolic pressure among the male and female groups and the lowest diastolic pressure of the female groups. Both systolic and diastolic blood pressure were significantly related to an interaction term between urinary Na excretion and pulse rate among males (P less than 0.02, P less than 0.03 respectively). These data support the hypothesis that psychological stress (assessed by pulse) and dietary sodium (assessed by sodium excretion) may interact to determine levels of blood pressure.