1. A comparison was made of the effects of starvation on available cellular energy in two crayfish species which possess different inherent metabolic rates associated with habitat adaptations. 2. Starvation for 45 days did not significantly lower phosphoadenylate concentrations or adenylate energy charge [AEC = (ATP + 1/2 ADP)/(ATP + ADP)] in dorsal tail muscle of either the epigean (surface) crayfish. Procambarus clarkii or the cave species, Orconectes inermis inermis. 3. After 5, 15 and 30 days of starvation, P. clarkii contained greater ATP and total adenylate concentrations in dorsal tail muscle than control crayfish which were fed. 4. The greater phosphoadenylate concentrations in unfed crayfish may be associated with increased motor activity previously documented in another surface crayfish species under conditions of starvation. 5. However, starvation did not induce changes in adenylate concentrations in O. i. inermis. 6. This could be due to the lack of sufficient nutritional stress to elicit a response in this more slowly metabolizing species.