Ten years after the discovery of prostacyclin, our knowledge of its biochemical mode of action, pharmacological properties, pathophysiological significance and therapeutic applications is ever expanding. Prostacyclin is both complex and unique as demonstrated by its unusual feature of being chemically and meta bolically unstable when compared to other prostanoids and known amine or peptide mediators. Although physiologically essential, the chemical instability of prostacyclin poses a serious drawback in laboratory and clinical studies. It is one of the genuine objectives of pharmaceutical research to supply synthetic compounds which overcome the inherent drawbacks - considering investigational and therapeutic use - of endogenous compounds. Whereas metabolic instability in certain cases could be of advantage, chemical instability definitely is not. With Iloprost, a molecule has been designed which - according to all data so far available - pertains high receptor affinity, metabolic instability (clinically this equates with a fine control of Iloprost's effects) while chemical stability has been achieved. By virtue of these characteristics Iloprost can be considered as one step towards specific interaction within the arachidonic acid cascade, namely the prostacyclin receptor. The aim of the symposium was to provide a critical experimental appraisal concerning the biochemical mode of action and pharmacological properties of prostacyclin and Iloprost.