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Metabolic cost, oxygen consumption (MO2, respiratory structure and body size interact to determine the capacity of salamanders for terrestrial locomotion. Salamanders respiring via both lungs and skin, Ambystoma laterale and A. tigrinum, or with skin alone, Desmognathus ochrophaeus and D. quadramaculatus, attained a steady-state MO2 during exercise in a treadmill respirometer. Endurance was correlated with the speed at which maximal MO2, was attained (VMO2.max). Low aerobic costs of transport (60–80% lower than reptiles of similar mass) increased VMO2.max. However, in lungless salamanders a low maximum MO2 decreased VMO2.max significantly. MO2 increased only 1.6- to 3.0-fold above resting rates in active lungless salamanders, whereas it could increase 3.5- to 7.0-fold in active lunged salamanders. Lungless salamanders attained maximal MO2 at half to one-tenth the speed of lunged animals. Lungless salamanders fatigued in 20 min or less at speeds that lunged salamanders could sustain for 1–2 h. Body size also affected the capacity for oxygen uptake during activity and locomotor performance. The large lungless salamander D. quadramaculatus attained maximum MO2 even at its lowest rate of travel. Cutaneous gas exchange does not provide lungless salamanders with gas transport capacities found in lunged animals. However, only small increases in MO2 may be required for modest levels of activity.