The main causes of parenchymal liver disorders in dogs and cats are drug induced toxicity (phenobarbital, potentiated sulphonamids, diazepam etc.), infectious agents (leptospirosis, coronavirus, toxoplasmosis etc.), herbal and dietary supplements, biologic toxins (aflatoxin), food additives (xylitol), chemicals, metabolic disorders (hepatic copper accumulation), neoplastic disorders, hypoxic/ischemic disorders and in the end, trauma. By its progress and severity, every disorder can be characterized as acute od chronic. As a result of unspecific clinical appearance and mild (or even subclinical) simptoms, it can happen very often that acute liver disease proceeds into chronic liver disease, which can be in case of cirrosis irreversible, but there is still recovery possibility in case of fibrosis. Concerning acute hepatitis, animals can recover completely if the proper therapy is maintained. Clinical significance depends on rate of disorder, and the more damage is present, the more signs can occur. Although symptoms are mainly unspecific, the most common are lethargy, leanness, PU/PD, jaundice, coagulation disorders, ascites. To diagnose parenchymal disorders of the liver, biochemical blood testing is inevitable, as much as sonography and radiography (which is less significant), but unfortunately, in many cases, this kind of disorders can be diagnosed only after pathohistological examination after liver biopsy