Rauscher murine leukemia virus-induced erythroid, lymphoid and myeloid cell lines were characterized with respect to the expression of differentiation antigens using a panel of monoclonal antibodies. The expression of differentiation antigens was measured in a two-step micro ELISA procedure. The cell lines express a number of early markers and lack a number of mature markers characteristic for the respective cell lineages. Moreover they express a number of surface markers which are not or only rarely found on their normal counterparts. The expression of differentiation antigens indicates that the cell lines investigated are arrested in an immature stage of differentiation. This observation implies that the Rauscher virus preferentially transforms early hemopoietic cells.