Effective energy cutoffs have been calculated on an IBM-7090 computer for cadmium, gadolinium, samarium, and boron filters as functions of filter geometry, the ratio of Maxwellian to epithermal flux (assumed to be 1/E), the lower energy limit of the 1/E flux, the energy corresponding to the Maxwellian most probable (modal) velocity, and filter thickness. The geometrical configurations were spherical (which on the assumptions made is equivalent to a beam flux case), cylindrical, and slab. By the use of two or three different filters (cadmium and gadolinium and perhaps samarium) it should be possible to detect resonances in the thermal to cutoff energy regions, in addition to measuring resonance integrals and thermal cross sections of unknown nuclides.