The genome of the multiple-embedded nuclear polyhedrosis virus (MNPV) of Lymantria dispar (LdMNPV) was partially characterized by restriction endonuclease analysis and a physical map was constructed using cosmid cloning and Southern cross blot hybridization. Using BamHI, BglII, EcoRI and HindIII, the size of the genome was estimated to be 88.5 x 10(6) Mr or 134.04 kbp. LdMNPV DNA was also analysed using methylation-sensitive restriction enzymes. The resulting restriction profiles suggested that extensive methylation did not occur at the nucleotide sequence recognized by HpaII and MspI. A BamHI restriction map was constructed by comparing overlapping BamHI fragments between cosmid clones containing partial digests of viral DNA. The positions of the BglII, EcoRI and HindIII sites were determined by Southern cross blot hybridizations and aligned to the BamHI restriction map. At least four homologous regions were identified by cross blot hybridizations of BglII-digested LdMNPV DNA and such regions were found to be interspersed along the genome in a fashion similar to that reported for other baculoviruses. Using recombinant plasmids containing the HindIII-V fragment of Autographa californica MNPV to probe Southern blots of LdMNPV DNA, the restriction fragment(s) that contain the polyhedrin gene were identified. Based on these findings the map was oriented with the polyhedrin gene of LdMNPV as the zero point.