The in situ deposition of Pt and Ir on CdS during the photocatalytic decomposition of aqueous sulfide results in the formation of an effective bifunctional photocatalyst (MS/CdS/M, where MS is Pt or Ir sulfide and M is Pt or Ir) which is more active than CdS and metallized CdS. In situ metallization provides a convenient method for the preparation of metal- and metal-sulfide-deposited CdS. The order of reactivity for the in situ metallization of CdS in the case of the photocatalytic decomposition of aqueous sulfide is Rh > Pt > Ru = Ir > Co ≃ Ni ≃ Fe. Based on the observed results a mechanism for the photocatalytic decomposition of aqueous sulfide is proposed. © 1995.