Synthesis, conversion, specific binding sites for PGI2, PGE1 and PGD2 and adenylate cyclase activity were evaluated in rat brain microvessels. All PG's investigated enhance adenylate cyclase activity dose-dependently. PGE1 and PGD2 were the major PG's formed by microvessels, in contrast to rat aortic tissue, generating predominantly 6-keto-PGF1 alpha, the stable degradation product of PGI2. On the contrary, RIA demonstrates that rat cerebral microvessels form predominantly 6-keto-PGF1 alpha (from endogenous precursor), followed by PGE2 and PGD2. PG actions on microvasculature are supposed to be predominantly mediated by adenylate cyclase linked receptors and there is good evidence for a central role of PGI2 and PGD2 in local regulation of the microcirculation.