An unusually severe localised corrosion attack on type 304 stainless steel panels exposed to the harbour waters of Bombay was observed. The present paper incorporates work carried out to understand the possible role of aerobic and anaerobic bacteria in promoting this localised corrosion. Aerobic (Comamonas testosteronii) and anaerobic (Desulphovibrio vulgaris) bacteria were isolated from corrosion pits underneath barnacles settled on 304 stainless steel coupons. Experiments were carried out using steady state potential behaviour, potentiodynamic anodic polarisation, AC impedance and multiple crevice corrosion techniques to ascertain the influence of the two bacterial species individually and in combination. The aerobic and anaerobic bacteria in combination were more aggressive than the individual species.