Uranium / U in biological materials / Laserßuorimetry Summary An improved rapid method for the determination of uranium in biological materials is described. Gram quantities of sample are ashed. The residue, after fuming with nitric and perchloric acids, is taken up in a Ca(N03)2 Solution and the uranium is extracted with methyl-isobutylketone (MIBK). After Stripping the uranium from the MIBK Solution into 0.001 M HNO3 it is measured with a laser fluorimeter type Scintrex® UA-3. A determination of the extraction recovery using a spiked sample is required. The results of the analyses of several commercially available uranium Standard materials are given.