Mole salamanders, Ambystoma talpoideum, are one of several species that exhibit facultative paedomorphosis. Many characteristics of paedomorphs and metamorphs have been compared in an effort to understand the ecological and evolutionary significance of facultative paedomorphosis, but few physiological comparisons have been made. We measured resting metabolic rates (oxygen consumption) of paedomorphic and metamorphic mole salamanders, under aquatic (both morphs) and terrestrial (metamorphs) conditions in an effort to compare maintenance energy expenditures of these phenotypes. There were no statistically significant differences in metabolic rates between morphs during aquatic trials. Under aquatic conditions, size adjusted oxygen consumption rates ranged from a low of 0.085 ml/h to 0.194 ml/h. There was a trend for oxygen consumption to increase with temperature, and at night compared to day, but significant interactions among time of day, temperature, and phenotype revealed complex responses. Most interesting, although metamorphs and paedomorphs had indistinguishable metabolic rates in water, both morphs in water consumed 2–4 times as much oxygen as did metamorphs in air. Our results suggest that metamorphs, while in a terrestrial environment, may expend significantly less energy for maintenance than aquatic paedomorphs.