The effect of polyethylene glycol (PEG) additives of various molecular weights (600-40,000) on the kinetics of palladium deposition is studied by means of chronoamperometry. Inhibition of primary nucleation by PEG is found and attributed to partial blocking of active centers. However, no correlation is found between blocking effect and PEG dissociative chemisorption characterized by potential shifts after introducing PEG under open-circuit. PEG is found to affect both morphology and bulk properties of Pd deposits. The former is characterized by measuring true surface area in combination with SEM and STM imaging. Bulk defectiveness as studied indirectly in hydrogen sorption experiments is found to increase with PEG molecular weight. To interpret the experimental data, the hypothesis of PEG effect on palladium secondary nucleation is applied. (C) 2005 Elsevier Ltd. All rights reserved.