A reproducible partial-thickness burn was inflicted on 100 albino guinea pigs. With the blister intact, the evaporative water loss from the burn surface was essentially the same as from normal unburned skin. When the blister was removed, the rate of water loss was initially more than 100 times normal, and it remained 20 to 50 times the normal rate throughout the first week. This high rate of water loss was associated with an increasing depth of wound destruction (from dehydration) and a thickening of the overlying crust. Microscopic examination showed that previously viable dermis was incorporated in this crust. The depth of dermal loss was negligible when the blister was left intact, and improved healing resulted. We believe it is important to leave burn blisters intact, whenever possible.