The utility of spot urine collections for uranium bioassay determinations was examined in a small cohort of depleted uranium exposed Gulf War veterans. Some members of the group are excreting elevated concentrations of urinary uranium resulting from the metabolism of retained metal fragments, the residua of several friendly fire incidents. Uranium determinations were performed on both 24-h timed collections and spot urine samples using kinetic phosphorescence analyzer (KPA) methodology. Results ranged from non-detectable to 30.7 mcg g(-1) creatinine in a 24-h collection. A creatinine-standardized spot sample and a 24-h uncorrected sample both correlated highly (R2=0.99) with a creatinine corrected 24-h collection, presumed to be the best estimate of the urinary uranium measure. This relationship was upheld when the population was stratified by uranium concentration into a high uranium group (> or = 0.05 mcg U/g creatinine) but for the lower uranium group (< 0.05 mcg U/g creatinine) more variability and a lower correlation was seen. The uncorrected spot sample, unadjusted for volume, concentration or creatinine had the lowest correlation with the 24-h creatinine adjusted result, especially at lower urinary uranium concentrations. This raises questions regarding the representativeness of such a sample in bioassay programs.