The determination of uranium in urine is used for the control of subjects at occupational risk particularly in the nuclear power industry. As the levels of uranium in the urine and plasma of healthy subjects without occupational risks are very low, a very sensitive analytical method is needed. Inductively coupled plasma mass spectrometry was studied for this purpose. It is a direct, reproducible and sensitive method which would be suitable for the control of uranium in subjects at occupational risk but not, under the conditions adopted, for precise quantification of normal plasma and urine levels, which are lower than the limit of quantification of 35 ng l-1.