The role of the atrial natriuretic peptide (ANP) in Na and water metabolism is well recognized. Much less known is the physiological importance of ANP in the metabolism of other electrolytes e.g. calcium and magnesium, which are presumably involved in the pathogenesis of active renal stone disease (ARSD). The present study aimed to assess the potential role of ANP in the pathogenesis of ARSD. Two groups of subjects were examined. The first one comprised 30 patients with ARSD (diagnosed according to Smith's criteria) while the second one consisted of 21 healthy subjects. Both groups were studied under bed rest (BR) and water immersion (IW) conditions. The examined groups were not different by age, sex, serum electrolyte profile (Na, Ca, Mg) and urinary excretion of Na, Ca, Mg and oxalic acid. Patients with ARSD showed significantly higher basal level of ANP and a significantly higher response of ANP secretion to IW as normals. In spite of this abnormality, patients with ARSD showed a similar increase in water, Na, Ca, Mg and oxalic acid excretion stimulated by IW as compared with normals. In contrast to healthy subjects, patients with ARSD showed no significant correlation between serum ANP levels and urinary excretion of Na, Ca and Mg. In addition, only patients with ARSD showed a significant positive correlation between serum ANP and urinary excretion of oxalic acid during WI. Results obtained in this study suggest, that ANP may be involved in the pathogenesis of ARSD.