We propose a combined model for investigating the interplay between a growing biofilm on a metallic surface and stress corrosion. The biofilm model incorporates both substrate dissolution, bacteria metabolism and biofilm development, making it possible to estimate the pH at the metallic surface. The biofilm model is base on the well-known Wanner-Gujer model, cf. [1] for biofilm development and applied to a metabolism involving pH, cf. [7,8,9]. Including pH in the metabolism makes it possible to estimate the pH at the substratum as a function of the biofilm thickness, which then can be provided as input to the biocorrosion model.