Studies of nucleopolyhedrosis virus infection in midgut cells of corn earworm and cabbage looper larvae indicate that cytoplasmic microtubules might be involved in the vectorial movement of nucleocapsids from the microvilli, where invasion takes place, to the cell nucleus, where replication occurs. Such an association between cytoplasmic microtubules and adenovirus has been shown in Hela cells. During a recent study of the pathway of nucleopolyhedrosis virus infection in the gypsy moth, an unusual relationship was observed between microtubules and nucleocapsids in infected hemocytes and fat body cells.Fourth instar gypsy moths were fed a lethal dose of nucleopolyhedrosis virus. Larvae died of virus in 11 to 12 days. At intervals beginning at 12 hours and continuing to 10 days post-ingestion of virus, hemolymph was collected and fat body was dissected from groups of larvae.