The plutonium concentrations in mixed-oxide fuel rods containing distinct sizes of particulate plutonium oxide have been determined using high resolution gamma-ray spectrometry. The fuel rod enrichments were in the range 2 to 2.5 wt% in natural UO2. Individual rod enrichments were determined to within ±0.1 wt% by comparison with a known standard. Differences in plutonium iso-topic composition were discemable also, in addition to the differences in plutonium enrichment. The technique provides an inexpensive nondestructive method of determining in situ plutonium composition and content of assembled fuel rods, for purposes of quality assurance and accountability control.