Microbes recovered from sediments, slime, tubercles, or corrosion coupons were characterized into functional groups, identified by fatty acid patterns and used in a flow-through test system. Test solutions were prepared as field conditions and supplemented with nutrients for the growth of microbes. Four-sided working electrodes were fabricated to simplify experimental design by combining four steel disks from the same stock into one probe. Concentric electrodes were made to simulate localized corrosion and study the effect of bacteria upon stability of localized corrosion. Electrochemical techniques such as: open circuit potential, electrochemical impedance spectroscopy, and galvanic current measurements were performed to evaluate the corrosion of mild steel in solutions containing different combinations of bacteria. Actual microbial community on the electrode surface was recovered by culture methods for viable counts upon termination of experiments. Preliminary results indicated that this test system provided an accelerated testing to simulate field exposures.