The effects of mercury exposure are determined by: (a) chemical form, (b) route of exposure, (c) dose, and (d) patient factors. Patient factors include age, genetics, environmental aspects, and nutritional status, and are responsible for different individual responses to similar doses. When blood and urine are collected to evaluate exposure, the results are influenced by (a) specimen collection, (b) analysis, and (c) the time elapsed from exposure. Interpretation is influenced by the patient's symptoms and is facilitated by comparison to published reports. The ranges reported in the literature are broad, with elevations as high as 16,000 microg/L in blood and 11,000 microg/L in urine. Interpretation is relatively straightforward when the results are massively elevated, but becomes increasingly difficult as concentrations approach the population norms (blood and urine mercury < 10-20 microg/L). Interpretation can be aided by biological markers (eg, urine porphyrins, beta2-microglobulin, and N-acetyl-beta-D-glucosaminidase).