The electrochemical deposition of spatially dispersed platinum centers within a tungsten oxide film onto the surface of a carbon substrate is described. The approach explores cathodic fabrication of metallic Pt microparticles via anodic dissolution of a Pt counterelectrode. Nonstoichiometric tungsten(VI,V) oxides are simultaneously electrodeposited with Pt particles during reductive potential cycles. We describe electrocatalytic properties of the resulting composite films toward reduction of dioxygen. We also demonstrate that a Pt-free tungsten oxide film shows strong electrocatalytic activity peroxide. for reduction of hydrogen peroxide. The method permits preparation of films containing platinum microcenters at low loadings (ca. 5 mu g cm(-2)) within the reactive oxide matrix We postulate bifunctional activity of the system in terms of promoting catalytic reduction of oxygen (by the traces of platinum) and reduction of any hydrogen peroxide intermediate [by the W(VI,V) oxide matrix].