Monoclonal and polyclonal antibodies were used to examine the expression of three erythroid developmental antigen systems in the chicken, Japanese quail, and quail‐chicken hybrid. Chicken fetal antigen (CFA), quail fetal antigen (QFA), and chicken adult antigen (CAA) each represent a series of cell‐surface glycorproteins associated with the development of avian hematopoietic cells. Monoclonal anti‐CFA antibodies from clones 190‐4 and 288‐1.1.1.2 supernatants were shown to react against epitopes associated with CFA determinants 8 and 2, respectively. Using complement‐mediated microcytotoxicity, these reagents permitted the identification of different erythroid subpopulations in the neonatal chicken and hybrid; therefore, heterogeneity in cell surface CFA determinants among mature peripheral erythrocytes should serve as a useful tool for analyzing erythroid development. In the case of CAA, erythrocytes from adult hybrids were found to express the same complement of CAA determinants identified in the chicken, and CAA appeared much earlier in the hybrid than in either of the parental species. Similarly, two species‐restricted fetal antigens associated with similar glycoproteins, CFA8 and QFA, had similar developmental profiles in their respective species, the chicken and quail. In contrast, these antigens were dominantly expressed but exhibited different developmental profiles on erythrocytes from the hybrids. While quail‐chicken hybrids exhibited apparent genomic interactions in the expression of these developmental antigens, no evidence for the existence of hybrid‐specific fetal antigens was obtained.