Supermolecular structure of drug delivery system on the basis of segmented polyurethane (SPU) has been determined to control the release of anticancer drug, cyclophosphamide (CPh). It has been established that the phase separation in SPU is essentially intensified by means of both the increase of molecular weight for SPU＇s soft segments and CPh incorporation in the monolithic systems of polyethylene glycol-based polyurethane. Infrared and proton NMR data indicate that CPh is hydrogenicly associated with a urethane group of hard segments. It has been determined that the drug-concentrated domains of hard segments are microheterogeneously dispersed in the amorphous soft segments. These results indicate that a supermolecular structure design of SPU allows for control of the CPh release from the polymer matrix. Medical-biological tests of the prepared polyurethane device have shown reduced toxic action of the cytostatic drug compared with injections. (C) 2000 John Wiley & Sons, Inc.