Cultured rat vascular smooth muscle cells from mesenteric artery produced prostaglandin (PG)E2, PGF2 alpha, PGI2 and thromboxane (TX)A2 in response to arachidonic acid, calcium ionophore A23187, vasopressin and angiotensin II. PGI2 was the major product among these PGs. PG synthesis in these cells decreased with in vitro aging, but the distribution pattern of PG synthesis did not change up to the passage level 56. Therefore, it is suggested that imbalance among PGs may not be directly implicated in vascular diseases in aging.