To determine the role of neuregulin (NRG)-mediated signalling in neuromuscular synapse formation, and to circumvent the problems associated with the early requirement for NRG-mediated signalling in early development, erbB genes were inactivated selectively in skeletal muscle cells, using the Cre/loxP recombination system. Two mouse lines were generated, mlc^creA and mlc^cre. mlc^creA and mlc^cre were crossed with mice carrying a floxed erbB4 allele (erbB4^flox). Results show that floxed erbB4 sequences were deleted selectively in skeletal muscle tissue, including the gastrocnemius, tibialis anterior and biceps femoris, but not in brain, liver, heart or stomach in mlc^cre; erbB4^flox/+ or mlc^creA; erbB4^flox/+ mice. Quantitation of the excision of the floxed DNA shows that 42-50% of the floxed DNA in skeletal muscle tissue is deleted in mice carrying either cre allele.