OBJECTIVES: Fibronectin (Fn) is a glycoprotein of extracellular matrix produced by a variety of mesenchymal and neoplastic cell types. BACKGROUND: In adult brain tissue, Fn is restricted to blood vessels. However, adult human brain cultures are almost entirely comprised of fl at or spindle-shaped Fn-positive cells usually referred to as "glia-like" cells. Since Fn is primarily present in fi broblasts, these cultures may be considered to be of non-glial origin. METHODS: Cells gained by long-term culturing of adult human brain tissue derived from brain biopsies obtained from 12 patients with non-malignant diagnoses were examined by immunofl uorescence methods. RESULTS: Primary cultures contained GFAP-/Vim+/Fn+ "glia-like" cells (95-98 %) and GFAP+/Vim+/ Fn-astrocytes (0.1 %) which disappeared by passage number 3. The formation of cell processes and enlargement of cell bodies was observed in 9 of 12 cultures with decreased cell growth during passages 12 to 17. It is remarkable that during this period, all "glia-like" cells became GFAP+/Vim+/Fn+. CONCLUSION: Herein, we confi rm our previously published hypothesis about the origin of adult human "glia-like" cells, which we consider to be precursor cells scattered through the brain cortex and subcortical white matter. Cultures were comprised entirely of GFAP-/Fn+ "glia-like" cells and showed morphological and immunochemical astroglial differentiation with spontaneously decelerated growth during prolonged passaging. We propose that the adult human brain tissue contains a "dormant population" of undefi ned glial precursor cells. Under culture, these cells show to have a high proliferative capacity and different stages of cell dedifferentiation (Fig. 2, Ref. 21).