"A first page Google result shows: "Studies performed at Doctors Data Inc. laboratory indicate that oral DMSA (30 mg/kg/day) for 1 to 3 days only yields about 1/5-1/10 the amount of mercury in the urine as does a single IV or oral dose of DMPS." http://www.mercout.com/pages.php?pageid=9"

Much of the mercury released by DMSA is through the bile and not through the urine(That is probably why there is much more concern about the possibility of kidney damage with DMPS rather than DMSA ), so just measuring mercury excreted through the urine is meaningless. It is almost as absurd as just measuring the fecal mercury excretion, and based just on that saying that DMSA works so much better than DMPS.

Let's just say that for many DMPS isn't even an option, however even for those who are able to use DMPS, imo it should only be used if DMSA has not worked for them.