Biofilm formation on metallic surfaces in marine and freshwater environments often precedes corrosion and other biofouling conditions. Attachment is mediated by such environmental factors as the presence of surface conditioning films, fluid dynamics, bulk-phase nutrient levels, and surface chemistry. In this study, we utilized a Fowler Cell Adhesion Measurement Module to demonstrate that the changes in cellular concentration and composition of a monoculture ofPseudomonas atlantica biofilms on stainless steel were a function of the applied shear force. At shear forces in the range of 3-10 dynes cm(-2) (1.0 liter min(-1)), attachment as measured by acridine orange direct microscopic counts was greatest at the higher shear forces.(14)C-Acetate uptake activity on the stainless steel surfaces increased with shear stress. Acetate incorporation ranged from 1×10(-5) to 19×10(-5) μmol cm(-2) between 0.15 and 30 dynes cm(-2) for 30 min uptake periods. On a per cell basis, however, activity decreased with shear, indicating a shift in metabolism. Fourier transform infrared spectroscopy revealed that protein and carbohydrate concentrations also increased with the applied shear. Increased biofilm C∶N ratios and total fatty acids were associated with the higher shear stresses. Neither radius of interaction nor biofilm age appeared to significantly influence the relationship between fluid shear and attachment and cellular composition ofP. atlantica biofilms in the range of 1-10 dynes cm(-2).