Prostacyclin is short acting and chemically unstable. To study sustained effects in an intact animal, prolonged intravenous infusion may be required. The compound has adequate stability for 24 hr in pH 10.0 carbonate buffer at 0 degrees. A "displacement syringe" is described wherein the prostacyclin solution is stored in a rubber bag inside the barrel of a 5 ml syringe. This device is placed in an ice bath. A syringe pump drives water into the barrel displacing an equal volume of solution out of the bag. Chronic venous cannules, saddles, and flow-through swivels are used as for drug self-administration studies. A simple, inexpensive rack for use with conventional individual hanging cages is also described.