The effects of vertebrate neurohypophysial nonapeptides (vasopressin, vasotocin and their synthesized analogs) on urinary magnesium excretion were studied in rats. Neurohypophysial hormones and their analogs at doses stimulating V 2 -receptors (0.0001-0.001 nmol/100 g BM) exerted antidiuretic effect and reduced urinary magnesium excretion. At higher doses, activating V 2 and V 1a -receptors (0.025-0.1 nmol/100 g BW), vasotocin and its analogs (deamino-vasotocin (dAVT), deamino-Thr 4 -vasotocin, deamino-hArg 8 -vasotocin, deamino-monocarbo-vasotocin) enhanced excretion of magnesium and sodium ions. A direct relationship was revealed between the enhanced renal excretion of sodium and magnesium ions under these conditions. After the V 1аreceptor antagonist injection, dAVT caused a 10-fold lower increase in magnesium excretion. The V 2 -receptor antagonist did not affect dAVT-induced magniuresis. The data obtained suggest that V-receptors are involved in magnesium transport regulation in the rat kidney.