Advances in the role of alloying tin on the electrochemical properties of lead alloys art: reviewed. In recent studies, the effect of tin on the conductivity of the passive layer developed on lead alloys has been studied by various techniques, e.g.. measurements of redox kinetics, cyclic polarization, a.c. impedance, chronopotentiometry, photoelectron spectroscopy. The results show that in pH 9 medium, the electron conductivity of the passivation layer, which is composed mainly of PbO, increases sharply when the tin content in the alloy is increased from I to 1.5 wt.%. Ln sulfuric acid, the tin content must be higher than 1 wt.% to ensure good electron conductivity of the passivation layer. A percolation mechanism is proposed to explain the modification of the conductivity. One of the effects of tin is to decrease the thickness of the PbO layer, during both the charge and discharge of lead-acid batteries. Tin dissolves slowly in sulfuric acid and this can explain thc decrease in the conductivity of the passivation layer after long polarization times. Alloying tin appears to favour the formation of an intermediate oxide PbOx, which is less resistive than PbO.