Abstract: Objective To examine the changes in energy metabolism in the respiratory muscles of canines with unilateral phrenic nerve transection using high-performance liquid chromatography (HPLC). Methods The left phrenic nerve of 8 canines was transected and the contents of adenine nucleotide in respiratory muscles were determined by HPLC before and 1 and 2 months after the operation. Results In the intercostal muscles, ATP contents remained almost unchanged during the entire course of the observation, while ADP content was elevated 2 months after the operation as compared with that measured before and 1 month after the operation (P<0.05). One month postoperatively, the content of total adenylic acid (TAN) decreased to the lowest point, but the difference between the measurements was not statistically significant; also at 1 month after the operation, the content of adenylate energy charge (AEC) was the lowest, with statistically significant difference from the measurements before and 2 months after the operation (P<0.05). In the diaphragm, the contents of ATP, ADP, TAN and AEC 2 months postoperatively were 9.05±12.70,2.99±2.57,14.72±13.98,0.57±0.29 from the levels at the other two time points (P<0.05). Conclusion After unilateral phrenic nerve transection in canines, the energy metabolism of the diaphragm declines significantly, whereas that of the intercostal muscle can be compensated to some extent.