Elasticity of living cells is a parameter of increasing importance in cellular physiology, and the atomic force microscope is a suitable instrument to quantitatively measure it. The principle of an elasticity measurement is to physically indent a cell with a probe, to measure the applied force, and to process this force-indentation data using an appropriate model. It is crucial to know what extent the geometry of the indenting probe influences the result. Therefore, we indented living Chinese hamster ovary cells at 37 degrees C with sharp tips and colloidal probes (spherical particle tips) of different sizes and materials. We furthermore developed an implementation of the Hertz model, which simplifies the data processing. Our results show (a) that the size of the colloidal probe does not influence the result over a wide range (radii 0.5-26 microm) and (b) indenting cells with sharp tips results in higher Young's moduli ( approximately 1,300 Pa) than using colloidal probes ( approximately 400 Pa).