A challenge test for mercury (and other toxic metals) using 2,3-dimercaptosuccinic acid (DMSA). A baseline urine mercury measurement is made followed by a further urine mercury level 2.5 hours after oral ingestion of 15mg/Kg bodyweight of DMSA capsules. All mercury levels are corrected for creatinine. Results can be useful in assessing an individual’s overall body load of mercury and for monitoring toxic metal chelation therapy. The test is also suitable for assessing body loads of some other toxic metals.