The overnight (12 h) urinary excretion of glycosaminoglycans, citrate, magnesium, calcium and uric acid were measured in 82 normal subjects and 63 outpatients who had formed at least one urinary stone. No significant difference could be found between the two groups of unselected subjects with respect to any of the urinary parameters. Nonetheless, recurrent stone formers had significantly lower glycosaminoglycans and predictive risk index than normal controls.