Abstract: A uranium-containing/metal binding complex and process for the determinat of natural and depleted uranium in biological samples such as water, urine, blood serum, saliva, amniotic fluid, cerebrospinal fluid, sweat, stool extract, synovial fluid, tears, semen extract, sputum, and peritoneal fluid. The samples are mixed with a buffer, one or more masking agents, and a solubilizing compound, to form a uranium-containing metal binding complex composition, followed by the addition of a pyridylazo indicator dye to said composition. The increase in absorbance due to the uranium-dye complex is determined with a spectrophotometer or colorimeter.