Hyperkalemia is a marker of many disorders in different species of animals and birds, leading to a significant number of pathophysiological abnormalities. However, dogs have no literature data on the features of potassium metabolism and etiological causes of hyperkalemia in different breeds, especially when taking into account significant differences in size and conditions of keeping. The purpose of the presented study was to identify and assess the frequency of occurrence of etiological causes leading to the development of hyperkalemia in dogs of different breeds in the territory of the city. St. Petersburg with subsequent statistical processing of the obtained results.In the presented study, the analysis of biochemical blood parameters of dogs of small breeds (Yorkshire Terrier, Toy Terrier, Pomeranian, dachshund, tsvergpincher, Chihuahua, Shih Tzu), large breeds (Labrador Retriever, German Shepherd, Dalmatian, American Staffordshire Terrier, Central Asian Shepherd, Husky) enrolled in private veterinary clinic of St. Petersburg in the summer-autumn period.It was found that the most common causes of hyperkalemia in small breed dogs include chronic kidney disease (25%), oncological diseases (18%), infectious processes (pyometra) (14%), heart disease (14%). In dogs of large breeds, the main role in the development of hyperkalemia is played by diseases of the urinary system – 24% (of which chronic kidney disease - 14%, acute renal insufficiency – 5%, bacterial cystitis - 5%), endocrinopathy - 19% (of which diabetes mellitus – 14%, hypothyroidism - 5%), oncological diseases (19%), orthopedic disorders (19%), neurological disorders (14%).