We have assessed whether adult human non-neoplastic astrocytes exhibit DNA synthesis in vitro, as measured using a double immunofluorescence technique to detect incorporation of 5-bromodeoxyuridine (BrdU) by nuclei of glial fibrillary acidic protein (GFAP)-containing cells. Dissociated cell cultures containing GFAP+ cells were established from surgically resected temporal lobe tissue from 3 young adult individuals operated upon to remove epileptogenic foci. In 5-18-day-old cultures from each of the 3 individuals, we observed GFAP+ cells whose nuclei had incorporated BrdU. BrdU nuclear staining was found in GFAP+ cells with either flat or process-bearing morphologies. The mean mitotic index for the GFAP+ cells was 6% (range 2-12%) as compared to a mean mitotic index of 29% for the GMK-7 glioma cell line. Our results do indicate that astrocytes derived from young adult donors, unlike such cells derived at autopsy from elderly adults, are capable of DNA synthesis in vitro, albeit to a markedly lesser extent than reported for fetal human astrocytes.