Measurements of the critical maximum (CTM), oxygen consumption, and heart rate of Plethodon neomexicanus and Aneides hardii were made for comparison with similar data for other members of the family Plethodontidae. At an acclimation temperature of 20 C, the mean CTM for A. hardii was 33.3 C, and for P. neomexicanus, 33.5 C. Mean oxygen consumption increased from 30.9 u1/g/hr at 5 C to 93.9 u1/g/hr at 25 C in A. hardii and from 35.4 u1/g/hr at 5 c to 60.9 u1/g/hr at 25 C in P. neomexicanus. The metabolism-temperature (M-T) curve for P. neomexicanus was similar to that of Desmognathus quadramaculatus, and eastern plethodontid, but the M-T curve of A. hardii was more comparable to that of a lunged salamander. Heart rate increase directly with temperature in both species. The mean heart rate increased from 22/min at 10 C to 64/min at 25 C in A. hardii and from 24/min at 10 C to 73/min at 25 C in P. neomexicanus. The low CTM recorded for these species may be related to the low temperatures characteristic of their microhabitat. The difference in M-T curves in these species may reflect differences in surface area-mass relationships resulting in differences in cutaneous gas exchange.