Some of the practical concerns associated with performing routine analyses of heavy metals (cadmium, lead, mercury, and arsenic) in various biological matrices are the selection of the biological matrix for monitoring, the sample collection, sample storage and shipment, and sample preparation and analysis. Other factors that affect the quality of the analytical values include contamination of sampling materials, blood drawing procedures, methods of obtaining urine samples, sample homogeneity, instrument calibration and performance, and laboratory quality control programs. A total system quality control approach is necessary to obtain accurate analyses of metals in biological samples, just as it is in all analytical situations.