In vitro neurovirological studies of viral infectivity or viral gene expression may be confounded by the multiple neural cell types and/or fibroblast contamination present in early passage cultures prepared from dissociated human central nervous system (CNS) tissue. We have developed highly enriched astrocyte cultures for neurovirological study by culturing in a serum-free defined medium, B16, supplemented with basic fibroblast growth factor (FGF-2). Subculture in this medium selects against fibroblast proliferation and favors sustained proliferation of a highly enriched glial fibrillary acidic protein (GFAP)-positive cell population. These astrocytes support productive replication of cytomegalovirus (CMV) and transient expression of transfected CMV and human immunodeficiency virus type 1 (HIV-1) viral promoters. By comparison, CNS cultures developed in standard serum-containing medium initially contain predominantly astrocytes, but show increasing contamination with fibroblasts with sequential passage. These cultures support CMV viral synthesis in both fibroblasts and astrocytes, cell types distinguishable only by immunostaining for cell specific antigen. CMV or HIV-1 promoter activities, quantitated by transient gene expression assays, are distinctly lower in CNS cultures maintained in serum-containing medium.