The formation of microbial biofilms on metallic surfaces was studied by combination of gravimetric, optical and electrochemical methods with high local resolution in dependence on colonization time and biofilm thickness. The use of electrochemical quartz crystal microbalance (EQCM) flowcells allowed simultaneous and continuous in situ monitoring of biofilm formation and resulting open circuit potential U-R. Combination of macroscopic and microscopic measurements Of U-R versus t with confocal scanning laser microscopy (CSLM) offered high resolution, destruction free characterization of the electrochemical influences of growing biofilms and their subsequent changes during disinfection and cleaning processes. Cyclovoltammograms (CVs) on macroscopic Pt electrodes after biofilm colonization proved a strong inhibition of H-adsorption and oxide growth while O-2-reduction was catalyzed. Repeated cycling reduced the biofilm effects until platinum behavior, except for the H-adsorption, could be observed again. Influences of biofilm thickness and age played an inferior role in these effects. Calculation of net charges showed a restriction of electrochemical detection to a sub-pin layer on the electrode surface. Microelectrode array measurements yielded no direct correlation between the localization of colonies and local shift of open circuit potential U-R for several film proportions. Disinfection with 70% EtOH killed the organisms, but left U-R unchanged. Cleaning with 10% H2O2 removed all biomass, resulting in clean microelectrode surfaces and restoration of U-R values to those of pure metal. (C) 2003 Elsevier Science Ltd. All rights reserved.