Semileptonic decays of heavy quarks yield prompt leptons which can be used to identify events resulting from the decays of the Z into c c and b b pairs. The procedures adopted to obtain clean samples of inclusive leptons with the ALEPH detector are described. Electron identification makes use of ionization measurements in the tracking system of ALEPH and the shape of showers in the electromagnetic calorimeter. Muons are identified using the tracking capabilities of the hadron calorimeter, together with the muon chamber information. Distinguishing the sources of prompt lepton production requires the determination of the lepton's transverse momentum with respect to the parent hadron's flight direction. As the latter is not directly measurable, the results of an algorithm are presented which uses the information produced by the ALEPH detector to achieve the most effective axis from which the transverse momentum should be measured.