The spectrum of lactate dehydrogenase (LDH) isozymes in erythrocytes of silver foxes was investigated by means of electrophoretic and immunochemical methods. By means of electrophoresis it is shown that differences in LDH isozyme spectrum between the animals homozygous for the gene Ldr-1a and those homozygous for the gene Ldr-1b are most conspisions at the age of 90-100 days of postnatal development. By means of the immunochemical method three groups of animals are distinguished differing in the LDH content in erythrocytes: the animals with a high LDH content (81.0 mcg/ml) and with a low LDH content (54.14 mcg/ml), which are homozygous for the gene Ldr-1b and Ldr-1a respectively, and the animals with intermediate LDH content (64.58 mcg/ml), which are heterozygous. The data obtained suggest that the effect of the gene Ldr-1a is associated with the decrease of the quantity of A subunits of LDH. It is assumed that the mechanism of the gene Ldr-1a action is realized either by means of the decrease of the synthesis of the A LDH subunits, or by means of the increase of the rate of their degradation.