It is well known that burst activity causes a rapid breakdown of muscle glycogen and extensive accumulation of lactate in frogs. During recovery, it has been shown that lactate is nearly totally recycled into muscle glycogen. Since catecholamines are likely to play some role in the regulation of postexercise repletion of muscle glycogen, the pattern of catecholamine response was assessed in frogs during intense physical activity and the ensuing recovery period. Chronically cannulated frogs were forced to swim until exhaustion, and serial blood samples were taken at regular time intervals for the measurements of catecholamines. The pattern of changes in plasma and muscle lactate and glucose and muscle glycogen during and after burst activity is similar to that reported in previous studies using noncannulated frogs, a result which indicates that the animals recover well from the surgical trauma associated with cannulation. The concentrations of plasma catecholamines in frogs at rest are comparable to those measured in other amphibians, and the levels of plasma epinephrine in resting frogs are much higher than those of norepinephrine. Burst activity causes a marked increase in plasma catecholamines, with higher levels reached by epinephrine. During recovery, the concentration of plasma catecholamines returns to normal within 30 min. Although this pattern of catecholamine response to intense physical activity may be favorable to the repletion of muscle glycogen postexercise, it remains to be clarified how critical the low levels and fast reduction in plasma catecholamines are for optimum glycogen resynthesis.