Concentrations of key metabolites were determined in carp white muscle before exercise and after maximal activity. It was found that the concentration of ATP decreases by about 65%, ADP decreases slightly, and AMP remains unchanged. Consequently, the level of the free adenylate pool decreases. Simultaneously there is an increase in the concentration of IMP and NH4+. The increase in IMP level and the decrease in adenylate pool are essentially in 1:1 stoichiometry, a result showing that the adenylate pool is decreased by the reaction catalyzed by 5'-AMP deaminase (EC 3.5.4.6 .). During exercise there is an increase in levels of glucose-6-phosphate, fructose 6-phosphate, and fructose 1,6-diphosphate that, along with the decrease in ATP levels, can account for the increase in glycolytic flux by activation of phosphofructokinase and pyruvate kinase.