Abstract: Disclosed herein is a novel baculovirus cloning system. The new cloning system is a marker-rescue system, using an essential gene, e.g. gp64. In this system, a gene essential for viral replication, growth, or propagation in cell culture is removed from or inactivated in the viral genome. Once a null baculovirus is created, it is propagated in a host cell that expresses the essential protein or a functional homolog. For cloning into the baculovirus containing the null-mutation, the virus is used to infect wild type host cells and the same cells are transfected with a plasmid that contains the essential gene, or a functional homolog, linked to a foreign gene under the control of a selected promoter. The baculovirus is "rescued" by the rescue gene linked to the foreign gene and is able to propagate normally and express the foreign gene.