Thirty healthy volunteers received piretanide SR 6 mg/day (n = 15) or placebo (n = 15) in a 10-day double-blind parallel-group comparative trial. 24-h urine output was significantly greater with piretanide than with placebo on D1 (1919 +/- 434 ml and 1160 +/- 335 ml respectively, p = 0.001 one-sided) as on D10 (1563 +/- 538 ml and 1236 +/- 435 ml respectively, p = 0.04 one-sided). Nevertheless the evolution of urinary output from D1 to D10 was significantly different (p = 0.008): it remained stable with placebo but diminished with piretanide. The diuretic effect of piretanide was apparent with a supplementary miction between 8 a.m. and 4 p.m. both on D1 and D10. Between 4 p.m. and 8 a.m., the number of mictions was the same in both groups. Thus piretanide SR 6 mg has a mild effect on the number of mictions; it should not alter patients' well-being.