An investigation of toner adhesion using a novel apparatus based on vibratory detachment of toners is presented. The toner size and toner charge dependences of the electrostatic and the non-electrostatic (or van der Waals) components of adhesive force are determined. The empirical relationship is consistent with the expression derived by Rimai et al. from the theory of Johnson et al. (the JKR theory). Based on this relationship, the requirements on electrophotographic process parameters for the use of small size toners are discussed quantitatively.