A discrete area of the anterior part of the subventricular zone, or SVZa, of the postnatal forebrain is composed of progenitor cells that are dissimilar to those elsewhere in the CNS. In vivo SVZa progenitor cells retain the ability for division, even though they are phenotypically neurons. To characterize further the properties of SVZa cells, we have analyzed their characteristics in vitro using cell-type specific antibodies and their proliferative capacity by the incorporation of bromodeoxyuridine. At 2 h in vitro, as well as after 1 day in vitro, virtually all SVZa cells isolated from the neonatal forebrain express TuJ1, an antibody that recognizes neuron-specific tubulin, and are GFAP-negative. Likewise, the preponderance of SVZa cells express the neuron-specific markers N-CAM and MAP-2 when examined after 1 day in culture. The majority of SVZa cells cultured for as long as 8 days also possessed a neuronal phenotype. In addition, process-bearing TuJ1-positive SVZa cells continued to proliferate throughout the entire culture period. Thus, the neuronal progenitor cells of the SVZa constitute a unique cell population with characteristics distinct from the cells of other germinal zones.