The purpose of this work was to determine the concentration and ratio of uranium isotopes in allied forces Gulf War veterans. The 27 patients had their 24-hour urine samples analyzed for 234U, 235U, 236U, and 238U by mass spectrometry. The urine samples were evaporated and separated into isotopic dilution and concentration fraction by the chromatographic technique. The isotopic composition was measured by a thermal ionization mass spectrometer using a secondary electron multiplier detector and ion-counting system. The uranium blank control and SRM960 U isotopic standard were analyzed by the same procedure. Statistical analysis was done by an unpaired t test. The results confirm the presence of depleted uranium (DU) in 14 of 27 samples, with the 238U:235U ratio > 207.15. This is significantly different from natural uranium (p < 0.008) as well as from the DU shrapnel analysis, with 22.22% average value of DU fraction, and warrants further investigation.