Blood lymphocyte, serum and urinary magnesium analyses were performed in a randomized group of 36 kidney stone-formers with the aim to determine the incidence of intracellular and extracellular magnesium depletion in urolithiasis. Lymphocyte magnesium depletion was found in 10 patients, serum magnesium depletion in 5 and concomitant lymphocyte and serum magnesium depletion in another 3 patients. Thus intracellular and/or extracellular magnesium depletion was found in 15 patients (41.7%). Oral magnesium supplementation (5-10 mmol Mg2+ daily) was found in some patients ineffective in both lymphocyte and/or serum magnesium repletion.