Manganese‐ and iron‐oxidizing bacteria (MFOB) are widely implicated in microbially influenced corrosion, often in association with sulfate‐reducing bacteria (SRB). Traditionally MFOB have been assigned a passive role in the corrosion process, promoting differential aeration cells, and providing oxygen depleted conditions conducive to the growth and corrosive attack of SRB. Recent work, summarized in this article, demonstrates that manganese biofouling alters the electrochemical behavior of stainless steel (SS), and suggests that MFOB are more active in localized corrosion than traditionally held. The paper discusses the chemistry and potentially corrosive impact of manganese and iron oxides on SS, explores the possible relationship between MFOB and SRB, and proposes a model to describe the synergistic influence these organisms may exert in the corrosion process.