The GP37 amino acid sequence of Spodoptera litura multicapsid nucleopolyhedrovirus (SpltMNPV) was compared with other baculovirus GP37, entomopoxvirus fusolin, the enhancing factor of Pseudaletia separata entomopoxvirus, and Alteromonas sp. chitin-binding protein 1. In these proteins, five 'conserved regions' previously reported constitute a chitin-binding domain. SpltMNPV GP37 effectively bound to purified crab shell chitin and the dissociation constant (Kd) for binding was 0.28 microM. Immunofluorescence analysis indicated that SpltMNPV GP37 was located in both cytoplasm and nucleus. Immunoblot analysis revealed that this protein was present in the envelopes of both occlusion body-derived virus and budded virus. Further analysis suggested that GP37 may bind to the chitin component of the peritrophic membrane of S. litura larvae.