Searches have been performed for neutrinoless muon-electron conversion and muon-positron conversion using a time projection chamber. An upper limit on the branching ratio for the coherent reaction R(1/4- +Tie-+Ti)<4.6×1 0-12 [90% confidence level (C.L.)] relative to ordinary muon capture was obtained. For the process 1/4-+Tie++Ca no events were observed for positron momenta p>96 MeV/c leading to an upper limit on the partial branching ratio relative to ordinary muon capture p>96(1/4-+Tie+ +Ca)/(1/4-+Ticapture) <9×10-12 (90% C.L.). With the assumption of a giant-resonance- excitation model the integrated limit would be (1/4-+Tie++Ca)/(1/4- +Ticapture)<1.7×10-10 (90% C.L.). © 1987 The American Physical Society.