Hello, It is hard to go blind on these issues. I have reviewed some threads and there is a lot of info regarding tests. The amount of info, limited ressources and energy make hard to decide, though. Thus, based on your experience, could you mention which tests you considered cost-effective and have been a turning point in your journey (diagnostics, treatment plan, benefits)? (I'll have to check additionally whether they can be performed by international shipping) GUT FUNCTION I understand a complete stool profile test is mandatory. @caledonia on her wonderful 4R summary suggests: Doctors Data Comprehensive Stool Analysis with Parasitology X 1 (often referred to as the CSA), and the Metametrix GI Effects Stool Test (I was told in another thread that Genova Diagnostics had bought Metamterix Lab and had changed this test) For leaky gut she adds: Genova Diagnostics Intestinal Permeability Assessment On my own search, I found Great Plains Laboratory which may be useful (and I have already checked I can perform it with a Dr. from my country), but I have not received any additional feedback so far, particularly from ME/CFS patients. MITOCHONDRIAL FUNCTION Claimed as THE area to support by many. Dr. Myhill's Mito Function Profile seems highly recommended by many and is shipped internationally. I suspect there are others competitive tests somewhere else, but I am not aware of. Suggestions are welcomed. GENES / METHYLATION Again, based on @caledonia's work: 23andME (sadly not shipped to my country) and Nutreval Test by Genova Diagnostics. RVK recommended Health Diagnostics Methylation Pathways Panel Thanks for your comments!