Urinary polyanions recovered from the urine samples of kidney stone-formers and normal controls were subjected to preparative agarose gel electrophoresis, which yielded fractions 1-5 in a decreasing order of mobility. In both groups, chondroitin sulfates were identified in the fast-moving fractions and heparan sulfates in the slow-moving fractions. Furthermore, two types of heparan sulfates were identified based on their electrophoretic mobility: slow-moving and fast-moving. The fractionated urinary polyanions were then tested in an in vitro calcium oxalate crystallization assay and compared at the same uronic acid concentration, whereby, the chondroitin sulfates of stone-formers and heparan sulfates of normals enhanced crystal nucleation. Fraction 5 of the normals, containing glycoproteins (14-97 kDa) and associated glycosaminoglycans, were found to effectively inhibit crystallization. Papainization of this fraction in stone-formers revealed crystal-suppressive effects of glycoproteins, which was not seen in similar fractions of normals. It was concluded that glycoproteins could modulate the crystal-enhancing glycosaminoglycans such as chondroitin sulfates of stone-formers but not in normals. The differing crystallization activities of electrophoretic fraction 1 of normals and stone-formers revealed the presence of another class of glycosaminoglycan-hyaluronan. Hence, in the natural milieu, different macromolecules combine to have an overall outcome in the crystallization of calcium oxalate.