During aestivation the metabolic rate of the Australian goldfields frog Neobatrachus wilsmorei was reduced by 80% from its standard metabolic rate. The in vitro rate of oxygen consumption of isolated muscle and skin from aestivating frogs was up to 50% lower than that of the non-aestivating frogs. This in vitro rate of oxygen consumption was maintained for 6-12 h, indicating an intrinsic metabolic depression of tissues during aestivation. Frogs became dehydrated during aestivation. Muscle, skin and liver also became dehydrated during aestivation, but brain and kidney did not. Na+ and K+ contents and extracellular space measurement for muscle indicated that ion gradients were maintained across the muscle cell membrane during aestivation. Increases in plasma concentrations of Na+ and K+ were matched with similar increases in muscle intracellular ion concentrations. Extracellular space measurements were unsuccessful in the other tissues, but K+ content in all tissues (per dry weight) was maintained during aestivation, and the concentration of plasma K+ did not increase above that which can be accounted for by dehydration, indicating that K+ gradients were maintained.