This invention relates to a stable epoprostenol composition that can becombined with commercially available IV fluids and can be administered in itsreconstituted and/or diluted form under ambient conditions of about 15-30oCfor greater than 24 hours. The composition preferably contains (a)epoprostenol or a salt thereof; (b) a alkalinization agent; and (c) a base,such that when reconstituted or in solution, the solution has a pH >; 11.Methods for making the lyophilized composition are also disclosed.