Astrocyte cultures from human fetal brain were infected with human immunodeficiency virus (HIV) either as free virus or with a chronically infected lymphoblastoid cell line and monitored for signs of infection. The lymphocytotropic strains HIV3B and HIVSF2(ARV-2) but not the monocytotropic strain HIVAda-M infected the human fetal astrocytes. The infected cells were monitored by immunocytochemistry, detection of p24 antigen in the supernatants and polymerase chain reaction amplification of the proviral DNA. No morphological or cytopathic effects were seen in these cells. Upon co-culture of astrocytes with a lymphoblastoid cell line chronically infected with HIVSF2(ARV-2), the lymphoblastoid cells readily adhered to the astrocytes as determined by a 51Cr adhesion assay and by light and electron microscopy. This cell to cell contact resulted in infection of increased numbers of astrocytes. Similar adhesion of lymphoblasts to microglia was not seen. Thus, astrocytes from human fetal brain can be infected in vitro directly by lymphocytotropic strains of HIV or by adherence to infected lymphoblastoid cells.