Uremic patients tend to have a lower than normal deep-body temperature. In addition, there is a clinical impression that uremic patients are also more thermolabile than healthy people; that is, in a warm environment, body temperature tends to be higher, and in a cold environment, body temperature tends to be lower than in healthy subjects. To test the hypothesis that uremia results in enhanced thermolability, nonoperated control (NO), nephrectomized (NX), and sham-nephrectomized (SHAM) rabbits were subjected to mild cold (5 degrees C) and heat (30 degrees C) stresses. At 48 hours postsurgery, the core temperature of NX rabbits was significantly lower than that of the NO or SHAM rabbits (P less than .01). Exposure to 5 degrees C resulted in a significant fall in body temperature of the NX (from 39.1 degrees C to 38.3 degrees C; P less than .05) rabbits compared to the NO rabbits. There was a tendency for body temperature of the SHAM rabbits to fall, and as a result, there was no significant difference in the change in body temperature between the SHAM and NX rabbits. Exposure to 30 degrees C resulted in virtually no change in the core temperature of the NO or SHAM rabbits, but did result in a significant rise in core temperature of the NX rabbits (P less than .02 and P less than .01 for respective comparisons), as well as a significant increase in mortality rate (P less than .02). Based on these data, we conclude that anephric animals are more thermolabile, and are less able to tolerate exposure to a warm environment, than are normal animals.