The ability of herpes simplex virus (HSV)-1 Glasgow (strain 17), HSV-2 (strain HG52), temperature sensitive mutants and a thymidine kinase negative mutant of Glasgow strain 17 to produce a cytopathic effect and induce viral antigen expression in primary and passaged human fetal brain cells was studied. No difference was detected between the behaviour of HSV-1 and HSV-2. Cell-type-specific markers and indirect immunofluorescence were used to define unambiguously the type of individual cells in culture. Cells characterized as astrocytes were present in passaged cultures. Neurons were only seen in primary cultures and were markedly nonpermissive for herpes simplex virus as defined by both cytopathic effect and antigen expression when compared with the other cell types. These techniques and observations are seen to have potential significance for a variety of clinical neurological and neurobiological studies.