Evening urinary oxalate excretion in stone formers.

Urine collections from stone formers and controls were made between 6 p.m. and midnight and analysed for oxalate content. No difference in oxalate output was found between these groups. This makes it unlikely that hyperabsorption of oxalate from the intestine is a common cause of idiopathic calcium oxalate stones. The convenience of 6-h urine collections for detecting hypercalciuria is discussed.