A comparison in mice has been made of the effectiveness of five chelating agents used clinically for acute mercuric chloride poisoning, or recommended for such use. The compounds examined were N-Acetyl-D,L-penicillamine (NAPA), D-penicillamine (DPA), 2,3-dimercaptosuccinic acid (DMSA), sodium 2,3-dimercaptopropanesulfonate (DMPS), and 2,3-dimercaptopropanol-1 (BAL). The test of effectiveness was their ability to reduce the mortality of acute mercuric chloride poisoning when administered 20 minutes after the mercury at chelate:mercury mole ratios of 10, 15, 20, and 30. All except BAL were found to be effective at the highest mole ratio tested, but N-Acetyl-D,L-penicillamine and sodium 2,3-dimercaptopropanesulfonate were significantly more effective than DMSA and BAL at mole ratios of 10:1. The relative effectiveness does not correlate with available data on stability constants. The toxicity of BAL itself becomes apparent at mole ratios of 20:1 and above.