Growth factor-mediated signal transduction is a process that is of fundamental importance in understanding cellular growth and differentiation. In order to elucidate the signaling pathways leading to neuronal differentiation, we have tried to identify intermediates that are selectively induced in the differentiation of immortalized neuronal hippocampal cell line H19-7. In the present study we found that immediate early gene cyr61 is expressed in a rapid and transient manner by bFGF during the differentiation of H19-7 cells. To clarify the signal transduction pathway for the induction of cyr61 by bFGF, we checked whether Raf-1 and mitogen-activated protein kinase (MAPK) is activated during the induction of cyr61. It is identified that cyr61 is induced by bFGF via at least two signaling pathways; MAPK-dependent as well as MAPK-independent signaling pathways. This study suggested that cyr61 is likely to play an important role in neuronal differentiation process.