The flavour changing neutral current (FCNC) decay induced by a Higgs boson in the standard model with three and four generations has been studied. This process occurs first at one-loop order, where it has been calculated neglecting the mass of the outgoing quark. The possibility of producing the as yet undiscovered Higgs boson H by this decay has been considered. In particular we consider the decay of a fourth generation b' quark; the FCNC decay b'→ bH may dominate the charged current (CC) decay modes if the b' mass is less than the top quark mass, for Higgs mass up to 60 Gev. The decay of the top quark, in the presence of a fourth generation, is also discussed
