The neuromuscular junction (nmj) is a commonly studied synapse, used often to investigate reciprocal signaling between a motor neuron and the appropriate target muscle. In Caenorhabditis elegans, ectopic nmjs can be created by eliminating selected embryonic muscle cells that act as guideposts for the migration of post-embryonic muscles. The ectopic muscles are required to induce sprouting from DD motor neurons, indicating the presence of a muscle derived signaling molecule that interacts with the neurons. A TGF-β homolog, unc-129, is reported to be transiently expressed in the dorsal body wall muscles. The timing of the expression of TGF-β coincides with the time that the DD motor neurons respecify their synapses. In this study, we show that TGF-β is expressed by the ectopic muscle and that in unc-129 mutant animals, the ectopic muscle is unable to induce sprouting from the DD motor neurons. Therefore, we conclude that TGF-β is necessary for ectopic nmj formation in C.elegans.