In order to make clear the packing mechanism of the BmNPV polyhedra, a polyhedrin gene negative recombinant baculovirus, vBmBac(polh-)-5B-EGFP, expressing EGFP was constructed, and used to infect BmN cells jointly with wild-type BmNPV. Fluorescent microscopic observation demonstrated that EGFP and polyhedrin were expressed simultaneously, and the EGFP expression and polyhedra formation occurred in most of the jointly infected cells. Analysis of the purified polyhedra from jointly infected BmN cells showed that the foreign proteins were present in the polyhedra. The results indicated that BmNPV polyhedrin could incorporate proteins other than viral proteins into the polyhedra. It implies that a nonspecific recognition mechanism exists in the embedment of BmNPV polyhedra.