  The most sensitive experiment to date to search for the muon and electron
lepton number violating decay $K^0_L \to \mu^\pm e^\mp$ has detected no events
consistent with this process. Based on this result, the 90% confidence level
upper limit on the branching fraction is $B(K^0_L \to \mu^\pm e^\mp) <
4.7\times10^{-12}$.
