One factor contributing to negative nitrogen balance in burned patients is protein loss through the burn wound. There is, however, little information on the amount and type of protein lost by this route. This study was designed to quantitate protein loss through burn wounds. Multiple full- and partial-thickness burns on 29 patients were studied. Sampled burn sites were dried and occlusive sponge dressings (2'' X 2'') were applied and left in place for 1 hour. The central 1 square-inch portion of the dressing was then removed, rinsed in distilled water, and total protein, albumin, and globulin were measured in the water wash. Considerable protein losses were measured. These losses were greatest in the first 3 postburn days, being somewhat greater in full-thickness burns (0.98 +/- 0.82 mg/cm2/hr) compared to partial-thickness burns (0.59 +/- 0.41 mg/cm2/hr) during this period mean +/- SD). Subsequent to the first 3 postburn days, protein loss in all burn types decreased to a relatively steady rate of loss of approximately 0.25 mg/cm2/hr. Based upon these data, average daily protein losses during the first postburn week can be estimated by the following equation: 24-hour protein loss through burn surface (gm) = 1.2 X body surface area (m2) X % burn (%). On subsequent days, protein is lost at approximately half this rate. These data demonstrate significant protein losses through burn wounds greater than recent studies have considered. It is possible that inadequate nutritional replacement of these protein losses is partly responsible for the marked negative nitrogen balance of the early postburn period.