Nickel-underpotential deposition (UPD) on platinum electrodes has been studied in sulphuric media using cyclic voltammetry. The process seems structure-related: among the surfaces we did study, only (2 × 1)-reconstructed Pt(1 1 0) surface yields nickel-UPD. At low pH values, nickel-UPD peaks overlap with the hydrogen adsorption/desorption region. At higher pH (2–3) the overlapping is less severe: nickel coverage increases and can be estimated. Nickel-UPD on platinum (1 1 0) is a slow and irreversible process. The co-adsorption of sulphate or hydrogen-sulphate anions is probable. Nickel-UPD on Pt(1 1 0) occurs even in the presence of CO. Nickel submonolayer on Pt(1 1 0) exhibit remarkable activity towards CO-oxidation.