An electron microscopic study was carried out on the morphogenesis of herpes simplex type 2 virus in BHK-21 cells BHK-21 cells was found susceptible to infection and replication of herpes simplex type 2 virus cytopathic effects of the herpes type appeared at approximately 1 day postinoculation. Foci consisting of rounded refractile cells and syncytia were observed. Projection of the nuclear membrane in the infected cells was also seen, Several infected cells showed a track-shaped structure which apparently consisted of multiple layered membranes of the nucleus.