We previously found that murine leukemia cells of T cell, B cell, and erythroid ontogeny express a cell membrane antigen that cross-reacts with an idiotype of an anti-retroviral antibody. In the present study, the expression of this antigen (termed AVID, for anti-viral idiotype) by murine erythroleukemia (MEL) cells was examined during chemically induced differentiation. AVID expression by MEL cells was found to be lost when they were treated with either dimethyl sulfoxide or hexamethylene bisacetamide, two chemicals that induce MEL cells to terminally differentiate. The kinetics of disappearance of AVID during inducer treatment reflected the kinetics with which the inducers caused MEL cell commitment to terminal differentiation. Loss of AVID expression by inducer-treated cells was inhibited by dexamethasone, which inhibits commitment and MEL cell differentiation. The subset of inducer-treated cells that expressed the least amount of AVID contained the greatest number of cells committed to differentiate. These results indicate that AVID identifies a novel differentiation antigen of MEL cells.