Cyanide adlayers formed on Pt(111) were investigated at submonolayer coverages under electrochemical conditions in sulfuric acid medium. For small coverage (θ) values, cyclic voltammetry indicates the formation of surface domains of adsorbed cyanide (islands). Great distances separate the islands in such a way that the reversible adsorption of sulfate/bisulfate ions takes place quite easily on this bare area. Simultaneously, the reversible adsorption of OH− ions occurs in the gaps between adjacent clusters of each island. Increasing the coverage of CNads results in a progressive diminution of the distance between islands and, consequently, to a decrease in the extent of sulfate adsorption. Conversely, the higher θCN, the larger the number of sites for OH− adsorption (higher number of rows between hexagonal clusters). Thus, the adsorption of hydroxyl species is enhanced at high cyanide coverage in this medium. Ministerio de Educación y Ciencia (PB97-0130); European Commission (CECA 7220-PR039)