We investigated the expression of mRNA for arginine vasopressin in vascular smooth muscle cells and A10 cells using reverse transcription-polymerase chain reaction and Northern blot analysis. Arginine vasopressin mRNA was identified both in rat aortic smooth muscle cells and A10 cells, suggesting that arginine vasopressin is locally produced in vascular smooth muscle cells. Arginine vasopressin, a potent vasoconstrictor, may modulate vascular function in an autocrine or paracrine fashion.