Sodium beraprost, a newly synthesized PGI2 analogue inhibited in a dose-dependent manner formyl-methionyl-leucyl-phenylalanine (fMLP) induced superoxide generation of human neutrophils, but it had no effect on the superoxide synthesis by phorbol myristate acetate (PMA) or A23187. Sodium beraprost inhibited Ca2+ influx in fMLP stimulated neutrophils employing fluorometry and confocal microscopy. These findings suggested that the inhibitory effect of sodium beraprost on fMLP induced superoxide generation was due to suppression of Ca2+ influx. To examine the relationship between the effect of sodium beraprost and phosphorylation of p47phox (the 47kDa cytosolic phagocyte oxidase factor), immuno-precipitation of p47phox and western blotting for phospho-amino acids were performed. Phosphorylation of serine residues of p47phox induced by fMLP was reduced in the presence of sodium beraprost in a dose-dependent manner. The reduction in phosphorylation was accompanied by a reduction in p47phox and p67phox translocation to the plasma membrane and superoxide generation. These findings suggested that p47phox phosphorylation was necessary for translocation and superoxide generation in fMLP activated neutrophils, and that p47phox phosphorylation was regulated by a Ca2+ dependent mechanism. These observations suggested that sodium beraprost inhibited fMLP induced superoxide generation of human neutrophils by the inhibition of p47phox phosphorylation and translocation by a Ca2+ dependent mechanism.