Neural crest cells are a transient population of cells which differentiate into multiple derivatives. How these derivatives become specified is not well understood but Sox10 is known to be important in many of them. We are interested in defining the precise role of Sox10 in zebrafish melanophores. Current evidence suggests that the only vital function that Sox10 performs in melanophores is to induce expression of the melanocyte master regulator mitfa (Elworthy et al. 2003). We explored a model for Sox10 function in melanophores, based upon a model for Sox10’s role in mouse sympathetic neurons (Kim et al. 2003), and tested the following predictions: as well as inducing expression of mitfa, Sox10 will repress expression of genes downstream of Mitfa thus, Sox10 must be downregulated, via Mitfa, to allow melanophore differentiation. We observed derepression of melanophore marker genes in sox10t3 mutants, supporting the hypothesis that Sox10 represses these genes in wild type melanophores. We documented Sox10/sox10 downregulation in developing melanophores and generated transgenic lines to test whether this is necessary for differentiation. Unfortunately our experimental lines did not express our transgene so we were unable to test this hypothesis. However, transgenic lines, generated as controls, which express CFP in melanophores or xanthophores will be useful tools in their own right. Finally we conducted RNA injection experiments to explore regulation of melanophore genes by Sox10 and Mitfa. We found that injection of mitfa induces expression of all our melanophore markers whereas co-injection of mitfa and sox10 does not. We also found that the 7.2 kb sox10 promoter contains six Mitf binding sites and is Mitfa responsive. Our data broadly support our original model but also suggest that it does not describe the complete network. We propose a modified model for the role of Sox10 in the genetic regulatory network controlling melanophore development.