Herpes simplex virus type 2 UL34 protein is expressed late in infection and is required for envelopment of nucleocapsids at the nuclear membrane and possibly at the endoplasmic reticulum (ER). It is a type II membrane protein with a C-terminal anchor that localizes mainly to the nuclear membrane in infected cells. However, in single transient expression, UL34 protein localizes predominantly to the ER. Relocation of UL34 protein from the ER to the internal nuclear membrane and the nucleus was observed in the presence of UL31 protein, a phosphoprotein known to interact physically with UL34. It is suggested here that interaction with UL31 protein is important for the nuclear targetting of UL34 protein and also that the trans-membrane region of UL34 protein is responsible for its localization at the internal nuclear membrane. The results also suggest possible sites for the interaction.