The sequence of the disaccharide units of eight heparan sulfate proteoglycans of different origins is described. All heparan sulfates contain 5 variable regions made of oligosaccharide blocks of disaccharides, namely, GlcUA(1-4)GlcNAc, GlcUA(1-4)GlcNS, IdoUA (1-4) GlcNS,6S,IdoUA-GlcNAc,6S, and IdoUA,2S(1-4)GlcNS,6S, besides two constant regions made of an internal tetrasaccharide (IdoUA-GlcNAc-IdoUA-GlcNS) and monosaccharides (GlcNS, and GlcNS,6S) at the non-reducing terminal. The N-acetylated region of the heparan sulfates is linked to the serine of the protein core through a trisaccharide of Xyl-Gal-Gal. Heparan sulfates differ from one another in terms of the number of disaccharides that compose each block.