The composition and degree of sulfation of glycosaminoglycans (GAG) in proteoglycans from various animal tissues were studied. It was shown that sulfated GAG contain chondroitin sulfates AC and B as well as heparan sulfates. The bulk of GAG in the majority of tissues under study is represented by 2-3 types of heparan sulfate molecules differing in the degree of sulfation. According to the degree of sulfation heparan sulfates from all tissues studied can be classified into three groups. Homologous tissues of various animal species are characterized by a similar composition and the degree of sulfation The data obtained are discussed in terms of the feasible role of proteoheparan sulfates in specific cell-to-cell interactions.