The basement membrane at the neuromuscular junction directs formation of pre- and postsynaptic elements at this synapse. Efforts to understand the molecular basis for development of the postsynaptic specialization have brought new insights into extracellular matrix proteins and their cell-surface receptors. Recent evidence for an agrin receptor and mice null for the s-laminin gene have reinforced the function of the basement membrane in both orthograde and retrograde signalling across the synapse.