The temperature sensitivity of herpes simplex virus type 1 (HSV-1) was assessed in primary cultures of mouse central nervous system (MNS) cells and mouse embryo cells (MEC). Infectious yields were determined and the ultrastructural morphogenesis of HSV-1 particles was compared following incubation at 37 or 40.5 degrees C. Yields of infectious virus were significantly reduced for both types of cell cultures following incubation at 40.5 degrees C. However, the effect of supraoptimal temperature (40.5 degrees C) on HSV-1 replication in MEC was significantly greater than the effect of supraoptimal temperature on virus replication in MNS cells. With respect to viral morphogenesis, no significant differences were found in either the quantity or the appearance (empty versus electron opaque core) of intranuclear particles present per infected nucleus, regardless of cell type or incubation temperature. However, complete virus particles (enveloped capsids with dense cores) were never observed in MEC at 40.5 degrees C, either intracytoplasmically or extracellularly. In contrast, complete virus particles were observed in MNS cell cultures at 40.5 degrees C, albeit in reduced numbers. At the permissive temperature (37 degrees C), complete intracytoplasmic and/or extracellular virus particles were associated with every infected cell in the MNS cell or MEC cultures. Thus an interactional effect on HSV-1 replication was found between cell culture type and incubation temperature.