I think I may have just stumbled across another piece of the puzzle. I was looking up the effects of Vitamin C on bacterial infections, and I found this: 'Intense or endurance exercise produces a concentration of endotoxin in the blood similar to that found in patients with sepsis. Oral ascorbate pretreatment of as little as 1 gram has been demonstrated to completely block the increase in circulating endotoxin and nitrite typically found during and after intense exercise30. It appears from this study that oral vitamin C prevents endotoxin translocation from the gut.' It was in this excellent summary of Vitamin C and endotoxin: http://www.vitaminc.co.nz/pdf/ENDOTOXIN-AND-VITAMIN-C.pdf, but the finding is from this paper: http://www.ncbi.nlm.nih.gov/pubmed/12885590 It seems to me that if this occurs in healthy volunteers, it is likely to occur to much greater extent in ME patients with leaky guts. It also seems to suggest that taking Vitamin C might have some effect on the severity of the PEM episode. If healthy volunteers need 1000mg though, it seems quite likely that ME patients would need more than this. If anyone has access to the full paper I would love to know more about it.