The work aimed to conduct a comparative analysis of clinical and hematological parameters in dogs and domestic cats with multiple organ pathology with primary liver damage (hepatic-renal syndrome) and primary kidney damage (renal-hepatic syndrome). The research carried out in veterinary clinics of Lugansk city. The authors found that regardless of the initial stage (kidney or liver) of polymorbid pathology in dogs and domestic cats, there is no significant difference between erythro- and leukocytopoiesis systems in experimental animals. The disease symptomatology does not allow differentiating variants of multiple organ pathology in dogs and cats both. At the same time, the ultrasound picture of the hepatic-renal syndrome characterized by the development of dystrophic changes and cirrhosis with foci of regeneration in the liver, signs of glomerulonephritis and nephrosclerosis in the kidneys. The same time in renal-hepatic syndrome, the development of acute tubular necrosis and interstitial nephritis was noted, nephrosclerosis in severe cases against the background of heterogeneous echogenicity of liver parenchyma and filling of the gallbladder. The hepatic-renal syndrome accompanied by pronounced cytolysis, hepatocellular insuficiency, cholestasis, hyperazotemia (an increase in urea by 1.5 and creatinine by 1.9 times) against the background of the absence of a significant interspecific difference between the levels of biochemical parameters in blood serum. Hyperfermentemia of AlAT and AsAT (2.7 and 1.8 times) was accompanied by creatininemia in cats and bilirubinemia in dogs.