A fixed-volume drop of liquid between a pair of parallel surfaces has been a common model for the denture-mucosa system. The reported one-term equation for the model, the derivation of which is suspect, implies that the acting force is inversely proportional to the square of the separation. Direct measurement of the force, however, showed that a better approximation is given by a two-term equation, with force varying as the inverse of the separation. The need for rigorous theoretical derivation is thereby emphasized. The experimental data suggest that a maximum retention force might occur for denture bases at separations of about 15 microns.