Increased evaporative water loss following thermal injury sometimes results in electrolyte abnormalities, negative nitrogen balance, and hypothermia. Because different biological dressings have been claimed effective in diminishing evaporative loss, a prospective study was designed to compare them. Cadaver allograft, porcine xenograft (sheet and meshed), and amnion were placed on 28 granulating wounds for twenty-four hours. Water loss was then measured with an Evaporimeter, revealing that in both full-thickness and partial thickness wounds, allograft was twice as effective as sheet porcine and five times as effective as meshed porcine or amnion. In the absence of available cadaver allografts, sheet porcine xenograft is a satisfactory substitute for use on granulating wounds to diminish evaporative water loss, while amnion and meshed porcine are less effective.