The hitherto made investigations on the retentivity of cobalt-chromium dentures show that this power depends on the elasticity of material and the angle between the retentive surface and the vertical. The objective of this work was to determine the influence of friction on the retentivity of a cobalt-chromium denture and to measure friction ceoficients of various contact surfaces. Friction coefficient was measured by a simple but original method. Obtained results show clearly that friction is an important factor for the retention of a cobalt- -chromium partial denture by cast clasp. Various contact surfaces have different friction coefficients (ju). Therefore, in the conclusion it is pointed out hat in planing the retention system of a cobalt-chromium denture the friction coefficient, i.e. the abutment tooth material must be taken into consideration.