It is known that exercise causes predictable physiological changes with corresponding changes in the components of the peripheral blood in many species. In some cases, these changes reflect the appropriate physiological adaptation to the demands posed by just exercising, while in the other cases they reflect pathophysiological abnormalities that result from the stress caused by exercise. The hormonal changes that occur during exercise affect the metabolism to cope with the energy demands of exercise. Energy sources other than glucose are fatty acids, which are stored by esterification ti triglycerides, and server as a reserve of energy. Cholesterol is a part of the cell membranes, allows the transfer of substances in and out of the cell, as a basic component of serum lipoproteins play an important role in the transport of triglycerides and is precursor of bile acids which are synthesized in the liver and are essential to fat absorption in the small intestine. In this investigation/study the concentrations of triglycerides and cholesterol were measured in the blood of twenty dogs at the beginning and at the end of a four-month training, during which the dogs were submitted to exercise on a treadmill three times a week for 20 minutes. Triglycerides values were, except in the two dogs, within the reference range, while total cholesterol concentration were higher in eight dogs. At the end of four-month training the slight decrease in triglyceride concentration was shown. At cholesterol levels we have found statistically significant fall of total cholesterol values at the end of the training. Even though four dogs had higher values than the reference values, they were still in three dogs lower than before the training. This can be explained by increased degradation of the cholesterol on bile acids, further dissolvation and consequently increased excretion.