Summary: In this study, middle-aged 11 cats and 7 dogs with chronic renal failure (CRF) and clinically healthy 5 cats and 5dogs were used. Clinical examination showed unkempt hair coat and dirty skin, dry and sticky mucous membranes, dehydration, weakness, reluctancy in walking, tiredness, oral ulcerations around premolar and molar teeth and halitosis. In haemotologic examination, increase in the number of reticulocytes and mean corpuscular volume (MCV), decrease in the PCVand erythrocyte count and increllSe in the percentage of the lymphocytes and neutrophils and the serum urea and creatinin values were fo und. A degenerative right shift was seen in the neutrophils. Escherichia coli, Streptococci spp., Leptospira spp., and Klebsiella spp. were detected in the microbiological examinations of the urine collected by cystocentesis. The foul-smelling urine. sign!ficant proteinuria (+ + + + +) and haematuria, and decreased urine specijic gravity (1007-1016) were observed in the physical examination. In the microscopic examinations of the urine sediment 5-20 erythrocytes, 10-20 leucocytes. abundant epithelial debris. 10-15 fatty globules, 7-8 triple phosphate crystals, and mucous fibrils were detected per microscopic field with mean rates. At electrocardiography, sinus arrhythmia. increase in width or height of the P-wave, prolongation of the P-wave and P-R interval were determined. Heart rate was also increased. On ultrasonography, irregular kidneys with hipoechogenic or hiperechogenic cortex and medulla were observed. In the pathological examination of the kidneys, glomerulonephritis, interstitial nephritis, nephrotic changes, cyst, hydronephrosis, and a primary tumor were diagnosed. It was not observed differences between the pathologicalfindings of the kidneys of cats and dogs. It was also found other visceral organ findings besides kidneys.