We describe a new transcutaneous electrical resistance method for measuring surgical wound healing which permits repeated measurements in vivo throughout the healing period. A saline-filled silver electrode was used to monitor the increasing ohmic resistance which accompanied the healing. Two validation studies were carried out. In the first study, histology on 16 rats showed that an intact stratum corneum was responsible for the high electrical resistance of skin, since lesions of the corneum markedly lowered the resistance. In the second study, electrical resistance readings of incisional wounds were taken repeatedly over 20 days in 13 rats: regression analysis showed that the healing slope for each incisional wound had a correlation coefficient r-value greater than 0.85. Moreover, all slopes were positive (p < 0.001) demonstrating that resistance increases as wound healing progresses and hence is a valid measure of healing. Test-retest resistance readings showed high reliability when measurements were repeated on the same wound (Pearson r = 0.94, n = 110). Hence we have shown that this new method is both valid and reliable. The device only monitors epidermal repair and gives no indication of wound strength. A modified device recently developed for humans has been used successfully on post-surgical wounds in numerous patients.