Interspecies genetic variability of Baikal seal was studied for 22 proteins encoded by 24 loci. Genetic variants have been detected in transferrin (TfA = 0.96; TfB = 0.04), postalbumin (PaA = 0.130; PaB = 0.870) and "slow" carboxylesterase (CrE-6A = 0.98; CrE-6B = 0.02). Low genetic variability is characteristic of species as well as of many other representatives of Pinnipedia order.