The baculovirus expression vector system has been used extensively to produce numerous proteins originating from both prokaryotic and eukaryotic sources. In addition to easy cloning techniques and abundant viral propagation, the system's insect cell environment provides eukaryotic post-translational modification machinery. The baculovirus display vector system provides a number of advantages over prokaryotic systems, allowing the combination of genotype with phenotype, enabling presentation of foreign peptides or even complex proteins on the baculoviral envelope or capsid. Baculoviruses permit larger gene insertions, are easily propagated, and can be grown to high titers. Furthermore, surface modifications of the viral capsid enable specific targeting. This strategy can be used to enhance viral binding and entry to a wide variety of both dividing and nondividing mammalian cells, as well as to produce antibodies against the displayed antigen. In addition, the technology should enable modifications of intracellular behavior, that is, trafficking of recombinant "nanoparticles," a highly relevant feature for studies of targeted gene or protein delivery. Also, the ability to incorporate reporter genes under transcriptional regulation of mammalian promoters enables transduction efficiency to be monitored in mammalian cells in vitro and in tissues in vivo. Luciferase molecules in particular are nontoxic and emit light in direct proportion to their number in mammalian cells. This provides a sensitive and rapid assay for quantification of transgene expression without the need for illumination with an external excitation source.