[en] Some ions produced in a cavity ionization chamber diffuse to the surface of an electrode of the same polarity as their charge, and they therefore do not contribute to the signal current. An equation for the diffusion loss of ions in parallel plate ionization chambers was derived by Langevin some time ago. It has been confirmed experimentally for air at various humidities that the decrease in output current agrees precisely with values obtained from the equations. In previous papers, we have derived both exact and approximate equations for back diffusion loss of ions in cylindrical and spherical ionization chambers. In this paper, we measure saturation curves for cylindrical ionization chambers to confirm the validity of the equation After correcting for volume recombination and also for small initial recombination, experimentally obtained diffusion losses are compared with the values obtained from the equations. (authors)