Since January 1981, we have used the Exacon thermometer to monitor skin temperature of 180 completely amputated digits during and after replantation surgery. When skin temperature on the first day after surgery was above 32 degrees, 153 of 154 replanted digits survived. In contrast, when skin temperature was 32 degrees or lower, 22 of 26 replanted digits failed. Data were analyzed by the Probit model, which indicated that skin temperature monitoring with 32 degrees as critical temperature is significant at P = 0.01. Also, critical temperature was tested in the range of 31.0 degrees to 33 degrees at intervals of 0.1 degree. We found the probability of predicting the viability for replanted digits is highest when skin temperature is 32 degrees or higher.