Biological Monitoring is the monitoring of a substance or its metabolite in the body. The presence of a specific substance or its metabolites can be measured in body fluids like saliva, urine, blood, tissue, nails and expelled air. The most commonly used tests are done on blood and/or urine. The tests are usually done at a certain time, e.g. end of shift or end of work week. The tests are performed by an accredited pathology laboratory. The substances listed in the Table 3 have known Biological Exposure Indices (BEI).Click here to access the Table 3 of the Hazardous Chemical Regulation (R 1179 of 1995)