Two methods were developed for the determination of 236Pu in 238Pu. One method involves the direct measurement of 236Pu in the presence of 238PuO2. The second method consists of an indirect radiochemical determination of the ratio of daughter products from 236Pu and 238Pu (i.e., 232U and 234U). Both methods produce similar results, although each has its own distinct advantages.