The gp37 genes of the Mamestra brassicae and Lymantria dispar multicapsid nucleopolyhedroviruses (MbMNPV and LdMNPV) have been identified and characterized. Both genes were similar to other baculovirus gp37 genes and to entomopoxvirus fusolin genes. Phylogenetic analysis showed that baculovirus gp37 genes and entomopoxvirus fusolin genes form two distinct and wellseparated clades. There was no evidence of recent gene transfer between the two groups. The gp37 genes also showed a distant similarity to bacterial cellulose-and chitin-binding protein genes, but the significance of this is unclear. MbMNPV and LdMNPV gp37 were both transcribed from consensus baculovirus late transcription start sites. MbMNPV gp37 was additionally transcribed from a putative early transcription start site. Tunicamycin treatment of MbMNPVinfected cells confirmed that MbMNPV GP37 is N-glycosylated. Confocal immunofluorescence microscopy revealed that the protein is located exclusively in the cytoplasm, probably in the endoplasmic reticulum.