[en] One of the most challenging experimental problems at LEP is the measurement of the weak couplings of the quarks. As is well known for lepton pair production, forward-backward asymmetries are very sensitive to these couplings. The problem of determining the jet flavour in order to measure such asymmetries is considered. Two methods are discussed: (i) measuring the charge of the jet which should reflect the quark charge with unfortunately large fluctuations. This could be a way to isolate Q=2/3 quarks (top) and measure the asymmetry for these tanti t pairs; and (ii) using leading particles to assign the jet flavour. It is known that, when E/Esub(beam) =x→1, the probability that the leading meson carries the initial quark with approach unity. The second method is discussed in detail. (Auth.)