Measuring~~$\mathrm{\mid }{V}_{ub}\mathrm{\mid }$~~at~~the~~LEP/SLC

We show that the observation of energetic charged leptons from semileptonic $B$-meson decays at the LEP and SLC $Z$–boson factories offers a unique opportunity to measure the quark mixing matrix element $\mathrm{\mid }{V}_{ub}\mathrm{\mid }$. We present various distributions of the $B$ decay products to show that the $b\to u$ decays can be cleanly separated from the $b\to c$ decays, with a signal of $O(100)$ events per million $Z$ bosons produced.