We have developed two novel antibody formats: Fcabs, in which antigen-binding sites are introduced into a human Fc fragment and mAb2s, in which additional binding sites are engineered into the Fc of an intact antibody.Fcabs allow small therapeutic antibody fragments to be isolated that retain all normal antibody functionalities (antigen binding, effector functions and long half life) while mAb2s represents an elegant way to create bi-specific antibodies.Examples will be described demonstrating the potential of these proteins as next generation therapeutic biologicals.