We have evaluated the urinary excretion of promoting (calcium, phosphorus, uric acid, oxalate) and inhibiting (citrate, magnesium, glycosaminoglycans) factors of crystallization in subjects with idiopathic hypercalciuria and calcium urolithiasis and in a control group. The examined children had a free diet and were drug free for the last 2 weeks. They were not affected by malabsorption, D-RTA, urinary tract infection, or urinary tract malformation (factors interfering with urinary excretion of citrate and oxalate). In the patients with calcium urolithiasis, the daily urinary excretion of oxalate was significantly higher (p less than 0.01), and the urinary excretion of citrate was significantly lower (p less than 0.001) than in the subjects with idiopathic hypercalciuria and in the control group. Among the subjects with idiopathic hypercalciuria, those aged 4-9 years had a significantly reduced, though in the normal range, urinary excretion of citrate as compared with those aged 10-15 years (362 +/- 189 and 503 +/- 198 mg/g creatinine/24 h, respectively; p less than 0.01). Our data show that hypocitruria may play an important role in the pathogenesis of urolithiasis in children with idiopathic hypercalciuria. In these cases, the urinary citrate excretion was not inversely related to age, as has been suggested by other authors.