An in vivo method of monitoring healing was tested incorporating an Evaporimeter measuring water evaporation; reepithelialization was detected through reestablishment of the water barrier. In the first study two wounds were created with a 2-mm biopsy punch on each of the backs of 15 rabbits and covered with occlusive and semiocclusive dressings. Water loss increased from a preoperative value of 6 g m-2 hr-1 to 55 g m-2 hr-1 after surgery. Water loss from the occluded site returned to baseline values in 9 days as opposed to 17 days for the semioccluded sites (P less than 0.05). The second study followed the healing of full-thickness 4 X 4-cm wounds in five rabbits treated with fine-mesh gauze and five treated with a human amnion dressing. Wound area and water loss were observed during the repair process. Visually measuring the wound area, the injuries appeared 100% healed on Day 30. The Evaporimeter continued to detect significantly increased water loss up until Day 45 when the original baseline values were reached. No differences were observed between the gauze and amnion groups. The Evaporimeter presents a simple yet accurate, noninvasive tool measuring the wound healing endpoint based on regeneration of the epidermal water barrier.