Avian erythroblastosis virus strain R (AEV)-transformed, cloned erythroleukemia cells from three different ages of SC strain chickens were analyzed before and after differentiation induced by 1.0 mM butyric acid for expression of chicken fetal antigens (CFAs) and chicken adult antigens (CAAs) and for hemoglobin expression. Immunofluorescent analyses show the loss of individual CFA determinants from erythroleukemia cells with induced differentiation, although there appeared to be no correlation between CFA loss and onset of hemoglobin production. Erythroleukemia cells were examined by cell surface labeling followed by immunoprecipitation with antisera specific to CFAs and CAAs. Erythroleukemia cells expressed CFAs and CAAs on their membranes that are not reported to be expressed by the target cell of AEV. The expression of CAAs and the enhanced expression of CFAs by erythroleukemia cells may be due to limited cellular differentiation, alterations in regulatory controls of genes coding for CFAs and CAAs, or increased levels of production of previously undetected CFAs and CAAs following AEV transformation. Control and induced erythroleukemia cells expressed CFAs and CAAs that differed both quantitatively and qualitatively from normal erythroid cells. Molecular weight variations of CFAs and CAAs observed in the erythroleukemia cells may represent glycolyzation differences between AEV-transformed cells and normal erythroid cells.