The main aim of the project was to study the effect of flow rate (shear stress), under different nutrient conditions on pre-attached bacterial biofilms. The combined effect of flow rate and nutrient supply had not previously been systematically studied, and the relationship between physiological activity, attachment and detachment, growth at a surface, and flow rate appeared to be very complex. Special experimental flow rigs were built for this project. Thin biofilms (monolayers of cells) were attached to test sections and these were placed in the flow rig. The biofilms were then subjected to different shear stresses at a known glucose concentration. The numbers of cells were small compared to the total volume of medium in the flow rig, and so the change in the substrate concentration during an experiment was insignificant. Radiotracers could therefore be used to measure substrate assimilation at various flow rates and substrate concentrations. It was hoped to produce a model which would explain the experimental data which was obtained, and assess how flow rate influences biofilm development and substrate uptake. However, the experimental results suggest that flow rate haslittle influence on glucose uptake by Pseudomonas fluorescens (the species used for this work), and that glucose uptake at various flow rates depends only upon the glucose concentration present in the medium. It is possible that the explanation for this lies in the complex mechanism of glucose catabolism which is reported for this species. A considerable part of this project was spent in establishing appropriate experimental techniques in order to make the required measurements for analysis of the biofilms in the flow rig.