The gene encoding the E2 peplomer glycoprotein of coronavirus mouse hepatitis virus JHM strain (JHMV) has been inserted into the genome of Autographa californica nuclear polyhedrosis baculovirus (AcNPV) in lieu of the coding region of the AcNPV polyhedrin gene. This recombinant virus produced E2 protein in insect cells under the control of the baculovirus polyhedrin promotor. The expressed E2 protein was shown in size and antigenic properties to be similar to the E2 protein produced in mouse cells infected by JHMV. The expressed E2 protein was glycosylated and transported to the cell surface; however, no proteolytic cleavage was detected in insect cells. The sera from rats immunized with partially purified E2 protein derived from insect cells reacted in immunoprecipitation and immunofluorescence experiments with the E2 protein produced in JHMV-infected mouse cells. The antiserum failed to neutralize the infectivity of JHMV. These results suggest that the E2 protein expressed by the recombinant baculovirus in insect cells is similar but not identical to the E2 protein produced in JHMV-infected mouse cells. The inability of the E2 protein expressed in insect cells to produce neutralizing antibody is discussed.