Neural progenitor/stem cells reside in the subventricular zone and dentate gyrus of the adult rat brain, which proliferate in response to several growth factors. Here we show that the neurospheres generated from the adult dentate gyrus and subventricular zone proliferate in vitro in response to fibroblast growth factor-2, but not epidermal growth factor. Likewise, extracellular signal-regulated kinase phosphorylation was stimulated by fibroblast growth factor-2, but not epidermal growth factor. Immunoblotting demonstrated negligible epidermal growth factor receptor content in these neurospheres, indicating that neural progenitor cells isolated from the adult rat brain are not responsive to epidermal growth factor in vitro, because of the lack of epidermal growth factor receptors and/or their signaling. However, the lack of response by epidermal growth factor in our study could be because of the culture conditions, and may not reflect the physiological condition.