  In models where lepton number is considered to be a spontaneously-broken
global symmetry a massless Goldstone boson, the majoron (J), appears. We
describe a procedure to explore the muon-electron-majoron coupling using the
results from mu-e conversion search experiments. To accomplish that, we
determine how the energy spectrum of the muon decay into an electron and a
majoron is modified by binding effects in a muonic atom. We find that the
future mu-to-e conversion experiments may be able to produce bounds on the
mu->eJ rate which are comparable with the present ones from direct searches.
