Uric acid is implicated in calcium oxalate kidney stone formation. Conspicuously so far, two hypotheses have been proposed: direct induction of calcium oxalate precipitation by uric acid, and uric acid as anti-inhibitor by binding urinary glycosaminoglycans (GAGS). The aim of this work is to evaluate uric acid and the relationship with GAGS in a group of patients with calcium oxalate lithiasis, and in a control group for detecting possible differences between the two groups. It was found that the lower concentration of GAGS in stone formers could impede their inhibitory activity on the heterogeneous nucleation of uric acid in calcium stone formation.