Neural progenitor proliferation, differentiation and migration are continually active in the rostral migratory stream of the adult brain. Here, we show that the receptor tyrosine kinase ErbB4 is expressed prominently by the neuroblasts present in the subventricular zone and the rostral migratory stream. The neuregulins (NRG1-NRG3), which have been identified as ErbB4 ligands, are detected either in the stream or in adjacent regions. Mice deficient in ErbB4 expressed under the control of either the nestin or the hGFAP promoter have altered neuroblast chain organization and migration and deficits in the placement and differentiation of olfactory interneurons. These findings suggest that ErbB4 activation helps to regulate the organization of neural chains that form the rostral migratory stream and influences the differentiation of olfactory interneuronal precursors.