To evaluate the nutritional value of a new military operational ration, meal, ready-to-eat (MRE), 27 soldiers were fed the ration as their only food during a 34-d field exercise at an elevation of 1800 m. Thirty soldiers given hot breakfasts and dinners and MREs for lunch served as control subjects. Measurements were made of body height, weight, skinfold thickness at four sites, urine volume and concentration, urinary zinc loss, hemoglobin, hematocrit, serum alkaline phosphatase activity, serum concentrations of albumin, total protein, ascorbic acid, folate, retinol, and Zn, and plasma pyridoxal phosphate concentration. The men fed only MREs experienced significant weight loss compared with those fed hot meals. Neither group appeared to be dehydrated. Hemoglobin and hematocrit values rose in response to increased elevation. Both groups of soldiers displayed normal values, indicative of acceptable nutritional status, of serum proteins, measured vitamins, and Zn.