Incorporation of small quantities of Zn (<5 x 10(20) cm(-3)) into FeS2 (pyrite) leads to a significant change of relevant photoelectrochemical properties: the width of the forbidden energy gap, the quantum efficiency for the generation of photocurrents, and the photocurrent spectrum. In addition, the photocurrent ratio for the electron transfer from I- and Fe2+, respectively, controlled by ion-specific reaction sites, is modified. The phenomena obviously result from a partial substitution of Zn for Fe in the pyrite lattice. Zn atoms on Fe lattice sites seem to be responsible for both the significant changes in the electronic structure and the restructuring of interfacial pathways for electron transfer. This interpretation is supported by state-of-the-art augmented spherical wave band structure calculations.