Ukraine is one of the world leaders in the number of cats among the country's population, and one of the most common diseases is panleukopenia caused by a virus of the Parvoviridae family, which is extremely common among viral diseases and causes significant moral damage to owner animals. Therefore, given the relevance of this issue, the result of our study is to clarify, supplement and summarize the data on hematological and biochemical parameters of blood and erythrocytopoiesis in panleukopenia of cats. The development and improvement of modern methods of immunoprophylaxis and treatment can significantly reduce morbidity and mortality. The study was performed in veterinary clinics of Zhytomyr and Kyiv, blood for the study was taken from the superficial vein of the forearm Anterbrachium, medial subcutaneous vein or subcutaneous tibial vein Saphena. Diagnostic tests to confirm feline parvovirus were performed using rapid tests VetExpert and ELISA and PCR for the presence of parvovirus antigen in private veterinary laboratories “BioSoft” and LLC “Bald” in Kiev. The complex studies carried out indicated that in cats (n = 24) with panleukopenia, changes in the morphological and biochemical composition of the blood are characteristic. A deviation from physiological limits was found, which mainly characterize the functional state of the liver, namely, an increase in the content of total bilirubin (P ≤ 0.01) and total protein (P ≤ 0.01), the development of pancreatitis – taking into account an increase in glucose concentration (P ≤ 0.05) and α-amylase hyperenzymemia (P ≤ 0.001), kidney damage as indicated by an increase in creatinine concentration (P ≤ 0.001) and urea level (P ≤ 0.01). In the course of the research, a slight decrease in indicators of the main erythrocyte indices was established, namely, a decrease in MCHC (P ≤ 0.05), which indicates the development of anemia. As a result of an experimental study of the morphological parameters of blood, a complex pathogenesis of the disease with panleukopenia with multiple organ failure and the development of pathological immunosuppression and hepato-pancreatic-renal syndrome was established.