Bone morphogenetic proteins (BMPs) induce autonomic neurogenesis in neural crest cultures and stimulate sympathetic neuron development when overexpressed in vivo. We demonstrate that inhibition of BMPs in the chick embryo bythe BMP antagonist Noggin prevents sympathetic neuron generation. In Noggin-treated embryos, the noradrenergic marker genes tyrosine hydroxylase (TH) and dopamine-beta-hydroxylase (DBH), panneuronal neurofilament 160 (NF160) and SCG10 genes, and the transcriptional regulators Phox2b and Phox2a are not expressed in sympathetic ganglia. Whereas initial ganglion development is not affected, the expression of the basic helix-loop-helix transcription factor Cash-1 is strongly reduced. These results demonstrate that BMPs are essential for sympathetic neuron development and establish Cash-1 and Phox2 genes as downstream effectors of BMPs in this lineage.