This investigation covers the separation and concentration of isotopes of the light gases. Separation of the isotopes was achieved by a system based on one phase of the adsorption phenomena; that of desorption. The gases nitrogen, argon, neon, and helium were adsorbed at temperatures below their critical values on charcoal and then slowly desorbed at and above their critical temperature. Mass spectrometer analysis of the final product showed that isotope ratios of helium and neon could be significantly changed.