The importance of calorimetric methods in the study of colloidal phenomena is illustrated here by analysis of the enthalpies of adsorption, at 35 degreesC, of two gemini and conventional cationic surfactants (12-2-12 and DTAB, respectively) on the surfaces of two silicas with different chemical properties. The values of the differential molar enthalpies of adsorption, corrected for the contribution of the dilution of the surfactant in solution, allow precise description of the adsorption process of the surfactants at the solid-solution interface.