A new technique for assaying uranium samples based upon the difference in the fission cross sections of uranium isotopes has been studied. In a test of this method, samples of uranium containing both 235U and 238U were bombarded with a beam of 0.5-MeV neutrons obtained from the 3H(p,n)3He reaction. The 0.5-MeV neutrons caused the 235U nuclei to fission but failed to activate the 238U because of its high fission threshold. Fission neutrons from 235U were detected by a recoil proton scintillation counter which used the technique of pulse-shape discrimination to reject pulses induced in the detector by gamma rays. The relative sensitivities of the apparatus to 235U and 238U were measured and the ability of this method to detect changes in the 235U content of a sample of uranium containing only a few percent of 235U was studied.