This invention relates to the field of recombinant antibody technology. It provides novel recombinant IgY antibody constructs for diagnostic and therapeutical applications. The bivalent antibody constructs display a heterotetrameric or homodimeric format stabilized by disulfide bonds. The constant heavy chain domains C.sub.H2-C.sub.H4 are partly or completely of avian origin, whereas the V.sub.H, V.sub.L, C.sub.L, and C.sub.H1 domains as well as the hinge region may be of avian origin or derived from any other species. The invention allows to combine the advantages of IgY antibodies with those of established mammalian monoclonal antibodies. IgY antibody constructs comprising nonglycosylated IgY constant heavy chain domains allow to reduce unwanted interactions with C-type lectins, e.g., in human sera. Furthermore, chimeric IgY antibody containing mammalian V.sub.H, V.sub.L, C.sub.L, and C.sub.H1 domains as well as a mammalian hinge region provide a higher molecular stability than IgY antibodies in acidic conditions and, thereby, are especially suited for peroral therapeutic applications.