The value of the shear coefficient K used in Timoshenko's differential equation for flexural vibrations of beams has been experimentally assessed. For specimens of rectangular cross-section, K has been determined over a wide range of inverse slenderness ratios and for up to the fifth harmonic overtone of flexural vibration. It is shown that the expression of K=(5+5 nu )/(6+5 nu ) and K=(6+12 nu +6 nu ²)/(7+12 nu +4 nu ²), where nu is Poisson's ratio, for rectangular and circular cross-sections respectively, yield excellent agreement between theory and experiment.