The Dejaguin-Landau-Verwey-Overbeek (DLVO) theory was used to examine the relationship between adhesion and dissimilatory Fe(III) oxide reduction. Adhesion of Shewanella alga BrY to hydrous ferric oxide (HFO) was correlated with ionic strength and thus was accurately described by the DLVO theory. Reduction of insoluble HFO was also correlated with KCI concentration. In contrast, there was no correlation between soluble Fe(III) reduction and ionic strength. A correlation between HFO reduction rate and adhesion to HFO was observed. These results provide direct evidence that adhesion is requisite for Fe(III) oxide reduction in the absence of soluble electron shuttles.