The isoelectric spectrum of albumin isolated from the liver and blood serum of 30-, 45- and 90-day rabbits was studied. By the method of isoelectric focusing in the boron-borate buffer--mannitol system. It is shown that the liver albumin displays heterogeneity ans is separated into four-five fractions, with pJ 4.8-6.0. Age peculiarities are found for the isoelectric spectrum of this protein. The serum albumin spectrum for rabbits of the studied age groups is characterized by the presence of a homogeneous peak with pJ 5.59, 5.57 and 5.47 corresponding to 30, 45 and 90-day age, respectively. Identity of serum albumin and protein of some liver albumin spectrum components is established by analyzing the pattern of the isoelectric spectrum for a mixture of preparations of 90-day rabbit proteins under comparison.