The helicase gene from Anticarsia gemmatalis multicapsid nucleopolyhedrovirus (AgMNPV) was identified and localized in the 58.85-65.90 m.u. of the viral genomic map. This gene encodes a putative polypeptide of 1221 amino acids containing motifs homologous to those found in the helicase superfamily. Expression of the AgMNPV helicase was observed as early as 4h post-infection (p.i.) up until 10 h p.i. A unique early transcription initiation site was observed upstream a putative TATA box. Phylogenetic analysis of the helicase genes of 23 baculoviruses indicated that the AgMNPV helicase is closely related to the helicase genes from Epiphyas postvitanna multicapsid nucleopolyhedrovirus and Choristoneura fumiferana defective nucleopolyhedrovirus.