A very simple analytical procedure with dimethylmethylene blue as photometric reagent was applied for the evaluation of glycosaminoglycan (GAG) urinary excretions and concentrations in both sexes, calcium oxalate stone formers, and a control group. The GAG concentrations varied significantly in stone formers (males and females) and in the control group; moreover, in some individual cases, a deficit of urinary GAGs was clearly detected. Apart from important inhibitory effects of GAGs on heterogenous calcium oxalate nucleation, the low urinary GAG content could be the cause of a pathological epithelium, favoring stone formation. The dimethylmethylene blue method is recommended as a quick screening procedure to determine a GAG deficit.