The expression of gp85, the major viral glycoprotein of avian tumor virus, by certain chicken embryonic cells was studied by the use of sera directed to antigenic determinants of subgroup E viral gp85. As analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of immune precipitates prepared with lysates of cells that had been labeled with [(3)H]glucosamine, chf(+) chicken embryo cells synthesize molecules of gp85 which possess type and probably also group antigenic specificities. Under similar conditions of analysis, no gp85 or antigenically related components could be detected in lysates of chf(-) cells.