A novel method for the synthesis of polyureas has been developed. This method involves ring-opening addition reaction of 2-phenyl-1,3,4-oxadiazolin-5-one with diamines, bis(4-aminophenyl)ether, 4,4'-methylenedianiline and m-xylylenediamine, followed by self-polycondensation of the resulting ring-opened adducts. Polymerizations in m-cresol at 150 degrees C proceeded fast and were almost completed within 5 h. Polyureas were produced with reduced viscosities up to 0,38 dL.g(-1). A model compound study was performed to demonstrate the feasibility of the reaction for the formation of polyureas.