The technique of accumulating plaque on removable disks in a complete denture provides a convenient method for investigating plaque on artificial surfaces. Examination of the plaque specimen with a SEM indicated that the plaque consists of microorganisms and a nonstructured matrix. This technique provides results that are consistent for a given individual. However, a group of 12 different individuals had a wide range in the thickness and content of plaque accumulations during equal time intervals. Thin plaque accumulations consisted of a filmlike layer with an apparently small number of microorganisms. Thick layers of plaque consisted of relatively large numbers of microorganisms with some intercellular matrix. The thickness of the plaque layer is apparently determined primarily by the number of microorganisms present.