Thirty men were studied during a 34-day intensive training exercise conducted by the U.S. Army. All soldiers were followed to determine the effect of such training, designed to simulate wartime operations, on selected zinc parameters. The soldiers consumed a nutritionally adequate diet made from fresh foods (A rations) prepared at the training site. Dietary intake, weight change, serum zinc, alkaline phosphatase activity, and urinary zinc excretion were measured. The 34-day intensive training exercise was associated with weight loss, depressed serum zinc levels, and elevated urinary zinc excretion. Alkaline phosphatase activity was not altered by the training exercise. The depressed serum zinc concentration could not be explained by the parameters measured. Weight loss was positively correlated with urinary zinc excretion. The functional significance of a depressed serum zinc concentration on performance deserves further study.