I'm new to this whole mercury thing. I'd never given it much thought because I've never had an amalgam filling, only composites (my mother was quite opposed to them even when I was a child!). My RBC mercury levels are pretty high according to my NutrEval results. My doctor says that RBC mercury usually reflects methylmercury in the body. This makes sense in my case since all of the mercury in my body comes from fish and the mercury in fish is in methylmercury form. I've seen some people argue that MethylB12 should not be used if someone has a mercury issue because cobalamin is known to methylate mercury and methylmercury can cross the blood brain barrier. However, I have also seen some studies (from the early 80s, one was from Sweden) where MethylB12 was the only form of B12 that was able to protect nerve cells from damage by methylmercury. So it seems like there is no consensus on this issue. Also, on a side note, I researched the mercury levels of citizens in high fish eating countries, such as Japan and Sweden. I tend to think of the citizens of these countries as being incredibly healthy. However, studies found that citizens of these countries had RBC mercury levels that averaged as high as 9 ug/g. For sake of comparison, the NutrEval puts the upper limit at 3.9 ug/g. Anyway, just food for thought. In my case, the mercury in my system is already methylmercury. So should I not worry about taking MethylB12 since my mercury is already methylated? It can't cause any additional harm, as far as I can see... My physician wants to concentrate on increasing my glutathione. She says that glutathione is what detoxifies mercury from the body naturally. If we can get my glutathione up, my body can excrete the mercury that has been building up from my fish intake. Though she did say that mercury interferes with raising glutathione levels, so it's a double-edged sword.