We examine the prospects for observing weak flavour-changing neutral current (FCNC) decays of B mesons at hadron colliders, including effects of anomalous W W Z vertices. Since it is very difficult to measure the inclusive rate B → X s ℓ + ℓ − one should consider exclusive modes such asEven though this requires one to compute hadronic matrix elements, we show that experimentally observable quantities (ratios of decay rates) are not strongly parametrisation dependent. Some possibilities for reducing the theoretical uncertainties from other experimental data are discussed.