The influence of polyethylene glycol derivatives on heparin release from cylindrical monolithic type silicone segment devices was examined in physical saline solution. This water-soluble carrier caused the devices to absorb the water in aqueous media. The release rate of heparin from the devices was increased as molecular weight of polyethylene glycol was increased. Water soluble carrier incorporated into silitone segment devices permits controlled release of heparin that otherwise would be released extremly slowly from the polymer. Heparin released from the silicone segment containing polyethylene glycol showed the first-order kinetics. Without changing the release-pattern, the release rate of heparin could be controlled by varing molecular weight of polyethylene glycol, the water-soluble carrier and depleting polyethylene glycol on the outlayer of devices. The mechanism of release probably showed the creation of pore or microdomine through the devices secondary to the swelling.