A flow cell system was used to assess the effects of shear stress and temperature on adhesion and retention of oral microorganisms from unstimulated whole human saliva. The saliva passed between two parallel mounted test plates, prepared and calibrated to present a surface energetic state similar to that of natural teeth and most restorative materials. The initial attachment of microorganisms occurred at a constant flow rate of 1 ml/min. Microbiota and biofilm material associated with the surface after 15 min of exposure were then challenged by introducing a cell-free rinsing fluid at increased flow rates. The remaining population was counted in a reflected light microscope and correlated to the calculated shear stress for each experiment. A reduction of 70-80% of attached microorganisms was seen after a 30-fold increase of the detaching force. No statistically significant differences could be detected in the proportions of initially attached or the remaining cocci and rods. The experiments were conducted at two temperature levels, both within a physiologic range representative of the oral environment. Temperature did not significantly affect the total numbers of attached or retained microorganisms, within the range of 22-37 degrees C. These findings demonstrate that non-specific attachment and detachment processes are important in the initial stage of microbial adhesion. Although biologically specific adhesive interactions were not addressed in this study, the data suggest that these may occur only after a minimum contact time of non-specifically surface associated cells.