Six materials (stainless steel, nickel-base alloy, titanium, chromium, nickel and admiralty brass) are tested in chemical and biochemical synthetic seawaters. The biochemical seawater contains enzymes catalyzing oxidation of glucose (glucose oxidase), simulating the action of natural biofilms. The evolutions of free corrosion potential (Ecor) versus time, and of cathodic and anodic reactions are compared with those obtained in natural seawater. Then, electrochemical behavior is related to semi-conducting properties of passive films. When glucose oxidase is present, increase of Ecor versus time is only reported for materials presenting a n-type semi-conductor passive film, and whose cathodic reaction current is increased. On the contrary, when passive layers are p-type semi-conductors, cathodic and anodic reactions are increased, and lead to a global Ecor constant with time of immersion. It appears that interaction between bacteria, medium and materials includes evolution of semi-conducting properties of passive layers. (C) 2003 Elsevier Science Ltd. All rights reserved.