The use of urine samples in biological monitoring was discussed. According to the authors, advantages of biological monitoring through urinalysis include the fact that this in a noninvasive procedure, that sufficient volumes of sample are available, and that the method requires relatively simple clean up procedures. The main disadvantage is the variability of urine outputs based on water intake and loss by the workers which is in turn influenced by the temperature and humidity in the workplace, as well as being influenced by drugs the worker may be taking. It is noted, however, that urine measurements should be used for exposure monitoring with caution. They should be avoided for individuals with significant impairment in renal function as manifested by elevated serum creatinine, diminished creatinine clearance, or proteinuria. The usefulness of biological exposure indices was discussed. Proper timing of the sample collection and the possibility of contamination are the main concerns. Tampering is also possible. Proper storage methods were discussed.