Homologues of almost all mammalian Ig-like immunoregulatory receptor families have been found in the chicken, except the Fc receptor (FcR) family. In addition to classical FcRs that specifically bind antibodies and mediate their effector functions, this family includes "Fc receptor-like" (FCRL) proteins for which ligands have yet to be identified. We have cloned and expressed a full-length chicken monocyte transcript that encodes an avian homologue of the mammalian FcR family. We have termed it chFcR/L as it possesses characteristics of both mammalian FcR and FCRL, but is phylogenetically distinct from either. chFcR/L is a transmembrane protein with four extracellular Ig-like domains and a short cytoplasmic tail. It can be expressed on the cell surface only in the presence of an accessory molecule, chFcRgamma, through which it acquires signalling potential.