The activities were studied in five kinds of enzymes (aspartate aminotransferase - AST, alanine aminotransferase - ALT, lactate dehydrogenase - LD, the thermally stable fraction of lactate dehydrogenase - LD-1, and alkaline phosphatase - ALP) of 30 male dogs. The dogs, divided into two age categories, were studied during a long-continued training (130 days). Both transaminases exhibit characteristic changes in the activity, with a depression at the beginning between the 30th and 40th days of training, followed by a slow increase in AST and by a rapid increase in ALT, continuing until the end of the training period. A statistically significant activity pattern was recorded in LD: the activity declined continuously in both age groups of dogs. LD-1 exhibited an activity depression continuing until the 70th day of training, followed by an increase which reached statistical significance towards the end of the training. ALP activity varied regularly, but always remained significantly below the starting values. The enzymatic activities can be used as partial tests during the scientific management of the training of dogs in relation to the physiological and pathophysiological processes in the bodies of the dogs subjected to the training stress.