Protein tyrosine phosphorylation is prevalent throughout the nervous system. It has been implicated to play an important role in the development and maintenance of neuronal functions. In the past few years significant advances have been made in our understanding of the molecular mechanisms of synapse formation and synaptic plasticity. Protein tyrosine phosphorylation appears to be important in the neuron-induced synthesis of the nicotinic acetylcholine receptor and aggregation of synaptic proteins at the neuromuscular junction during development. In addition, protein tyrosine phosphorylation may regulate the ion channel activity of the nicotinic acetylcholine receptor.