I have investigated the phenomenon of neural crest regeneration in the chick embryonic hindbrain using cellular and molecular markers as a model for the study of dorso-ventral patterning. By comparing and contrasting the expression of a number of genes - Pax-3, Pax-6, slug, dorsalin-1, Bmp-4, Bmp-7 and examination of the neural structures of the hindbrain in normal and ablated hindbrain, the critical events of repair and re-patterning were determined. The predominant finding was that the dorso-ventral pattern of the hindbrain was reproduced despite the removal of the dorsal third of the neural tissue. In agreement with other studies this indicates that dorsal and ventral signals coordinate to produce the spectrum of cell types in this axis. Additionally I found that slug and Pax-3 marked apparently independent lineages. Despite the normal re-patterning of the hindbrain after ablation this does not appear to have occurred by a recapitulation of normal development. That is, the sequence of gene expression (slug and Pax-3) resembles the trunk rather than the head, with slug expression being dependent upon closure of the ablated neural tube. This up-regulation of slug in cells of the dorsal midline correlated with the down-regulation of Pax-3 in the same population of dorsal midline cells, indicating that the exclusivity of these two genes may be obligate. To investigate this observation evidence of slug expression in the chick limb and other regions of the embryo was utilised. In the course of a range of experiments (in collaboration with K. Kostakopoulou) I found that slug expression was up-regulated by fgf-4 protein and down-regulated by ridge removal or retinoic acid addition in the wing bud. Thus, slug expression correlated positively with growth and the undifferentiated state and negatively with the onset of differentiation (condensation of progress zone cells). To conclude, slug and Pax-3 are expressed in non-overlapping, but neighbouring domains in the neural tube and represent lineage markers with very different characteristics; Pax-3 marks predominantly myogenic and neurogenic lineages and slug pre-skeletogenic.