The electrophoretic separation of isoenzymes of lactate dehydrogenase (LDH, EC 1.1.1.27) was performed in the kidneys, skeletal muscle, lungs and spleen in mink Neovison vison Schreber and blue fox Alopex lagopus L. pups at 15, 25, 60, 90, 120, 150, 180, and 210 days of age. Significant changes in the isoenzyme spectra of LDH in the tissues of mink and blue fox pups were observed in the initial period of the animals’ intensive growth and development –at the age of 15–0 days. In the skeletal muscles, lungs and spleen, the content of M-subunits of LDH during postnatal ontogeny was higher in mink than in foxes. The isozyme profile of renal LDH in 4‑onth-old pups of mink and blue foxes corresponded to that of 7‑onth-old animals. The tissue specificity of the LDH isoenzyme pattern reflects the metabolic profile of the tissues and is detectable already in early developmental stages.