Glycosaminoglycans (GAGs) are suspended in urine and are present on tissue surfaces in the urinary tract. Consequently, they have the potential to influence any pathological disorder in this environment, including urinary tract infections by Proteus mirabilis and struvite (NH4MgPO4.6H2(0)) urolithiasis. Although GAGs, suspended in urine, may inhibit the formation of other types of calculus minerals, no such effect has been reported in struvite calculi. Nevertheless, GAGs are a major component of the organic matrix of all types of urinary calculi. In contrast, there is evidence that the GAG layer on the bladder surface may act as a defence mechanism against infection by inhibiting bacterial adhesion. More studies are needed to elucidate fully the role of GAGs in urinary infections and struvite urolithiasis.