Due to the more detailed knowledge of prostaglandin metabolism in the recent past increasing interest was focused onto dipyridamole acting as platelet active substance. It was the goal of this study to investigate whether dipyridamole is able to exert any effect on vascular PGI2-synthesis. It is demonstrated that dipyridamole has a dose-dependent (0.1-100 microM) increasing effect on PGI2-synthesis or 6-oxo-PGF1 alpha-levels, respectively (the stable metabolite of prostacyclin). At a dose range of more than 10 microM this increase reaches the level of significance. Assuming that PGI2 acts as a local hormone in the vascular system this effect on PGI2-synthesis stimulation might contribute to the knowledge of the in vivo action of the substance.