The paper presents the results of the study of morphofunctional parameters of platelets in dogs with parvovirus enteritis at different ages. The most strongly expressed change of platelet parameters at parvovirus infection is in puppies aged 2 to 6 months. On the third day of the disease the number of platelets decreases and platelet disaggregation index under the action of ristomycin as well. On the fifth day of the disease there is a progressive decrease in the number of platelets with a decrease in platelet crit (PCT) and an increase in mean platelet volume (MPV), platelet disaggregation decreases under the influence of collagen and ristomycin, which is a sign of increased functional platelets activity, and in particular its vascular component. Changes of platelet parameters in the groups of dogs older than 6 months appear only on the 5. day of illness and are expressed by a reduction of disaggregation under the action of ADP.