A five-member team from the International Atomic Energy Agency in Vienna conducted a plutonium inventory verification at Argonne National Laboratory in February 1976. The presence of 45.706 kg of total plutonium, 88.184% fissile, was demonstrated as a substitute for Japanese-owned plutonium held in almost inaccessible storage by Westinghouse. An attributes check made by gamma counting and a variables check made calori-metrically verified to 95% certainty that the inventory was not smaller than the book value by 2.4% or more. It was estimated that 200 man-hours went into the effort. There were only a few minor snags, and those involved found it an interesting and instructive experience.