The dsDNA genome of 'Choristoneura fumiferana' nucleopolyhedrovirus (CfMNPV) was sequenced and analyzed in the context of other group I NPVs. The genome was 129 609 bp in length with a G + C content of 50.1%. A total of 146 ORFs of greater than 150 bp and with minimal overlap were identified. In addition, four homologous regions (hrs) were identified which contained 7-10 repeats with a 36 bp imperfect palindromic core. Overall, CfMNPV was most similar to OpMNPV based on gene content and arrangement and overall amino acid identity. Comparison with other completely sequenced baculovirus genomes identified eleven ORFs that were unique to CfMNPV. One of these, ' Cf103', encoded a protein with a putative zinc-finger domain. ' Cf103' was further characterized in terms of transcription and was found not to be essential for CfMNPV replication in tissue culture.