Forty-two patients with calcium calculi were selected based on calciuria > 0.1 mmol/kg/d on an uncontrolled diet. To measure excretion of sodium, calcium, phosphates and hydroxyproline, a 24-hr urine sample was collected on the 4th day of a milk product-free diet, a fasting urine specimen was collected on the morning of the 5th day and another sample was taken 4 hr after the oral administration of calcium. On the 5th day, plasma levels of calcium, phosphates, intact parathyroid hormone (PTH), calcidiol and calcitriol were determined on an empty stomach and after administration of a calcium load. The results, compared to those of healthy subjects evaluated under the same conditions, enabled classification of the stone-formers as having dietary hypercalciuria (n = 18), when calciuria returned to normal on a low calcium diet, and idiopathic hypercalciuria (n = 24), when the urinary calcium level remained high. Patients with idiopathic hypercalciuria were then classified, according to Pak's criteria, as having absorptive hypercalciuria (n = 8), when the fasting calciuric levels was normal, renal hypercalciuria (n = 1), when fasting hypercalciuria with elevated circulating PTH was controlled by a calcium load, or undetermined hypercalciuria (n = 15) for those individuals with fasting hypercalciuria and normal plasma PTH levels. In addition, vertebral density was measured tomodensitometrically and expressed as a percentage of the normal as a function of sex and age based on a regression line calculated with the results of 239 normal subjects.(ABSTRACT TRUNCATED AT 250 WORDS)