Recent experimental investigations have redefined the spectrum of growth factors and developmental signalling pathways that are necessary to orchestrate the growth and differentiation of regional neuronal subpopulations. Gene knockout studies of the classic neurotrophins and their high-affinity tyrosine kinase (Trk) receptors have refined our definition of the cellular mechanisms and target populations of these neuronotrophic factors. Recognition of the significant parallels that exist between neuropoiesis and hematolymphopoiesis has fostered our study of the range and cellular actions of these hemopoietins in neuronal development. In addition, by activating receptor subunits that possess serine/threonine activity, bone morphogenetic proteins of the transforming growth factor-beta superfamily exhibit complex spatiotemporal regulation of regional neuronal subpopulations. These collective observations suggest that a complex hierarchy of epigenetic signals is required for the growth and maturation of regional neuronal lineage species in the central and peripheral mammalian nervous system.