Twenty type A male students were compared to nineteen type B male students (all in apparently good health), before and after exposure to combined stress (noise and task). Before stress, red blood cell (RBC) Zn concentration is higher (P less than .05) and Zn excretion lower (P less than .05) in type A than in type B people. After stress, type A subjects exhibit changes that are larger and more significant than those of type B individuals. After stress, the type A group shows an important increase of urinary catecholamines (P = 2.10(-5), serum free fatty acids, and urinary Zn (P = .001); a slight increase in plasma magnesium (P less than .05); and a small but significant decrease in RBC Mg (P less than .02). These results suggest that type A subjects are more sensitive to stress than are type B people and more readily lose their intracellular Mg, the rise in plasma Mg being a transient one, probably consecutive to the cellular loss. The present observations are in good agreement with published data: ie, the psychological characteristics of type A personalities; their greater susceptibility to ischemic heart disease, which has been associated with Mg deficiency; the possible role of hypomagnesemia in the pathogenesis of hypertension and coronary vasospasm; and the high RBC Zn levels found in hypertensive patients.