For those radio elements whose beta-ray spectra have been adequately investigated, the average kinetic energy Ep is computed by graphical methods. Ep is calculated also" as a function of the atomic number Z and the spectral limit B, by means of Fermi's theory for allowed transitions, and compared to these experimental results. It is found that only the well-known experimental values of Ep for the forbidden spectrum of RaE deviates very markedly from the calculated one.