Hi, Hellen --
Welcome to the Forum! As has been pointed out, the only way to get official answers about the Challenge (and Challenge-related claims) is to send an email to
[email protected].
I've never heard of Mr. Vithoulkas, so I can't say anything for certain (and certainly don't speak for JREF); however, I've been watching the Challenge for a while so I can offer you some speculation.
One of the hardest things about the Challenge to grasp (especially for homeopaths) is that the results have to be unambiguous. That means there can't be any subjective judgement required. And the results have to be completely self-evident. It's very hard to do this with many homeopathic claims. For example, let's say someone claims that he can cure headaches with a 30C dilution of Pure Essence of Widget. The hard thing about this is: how can you demonstrate that anyone involved actually has a headache? Sure, they could /say/ that they have headaches, but how can you be sure? It's a subjective thing.
Many attempts to demonstrate homeopathy require, essentially, large-scale medical trials. This is generally out of the scope of the Challenge because of the time and resources it would require, all of which have to be paid for by the claimant. You'd have to have a really large pool of people. It's not to say that it's impossible; however, it's generally beyond the scope of claimant's ability to arrange.
Some simpler demonstrations have been suggested: in particular, check out Homeoproofer's Challenge thread. In particular, he claims (or claimed, at one point) to be able to distinguish between an ordinary container of solvent and a container of solvent with a 30C (or greater) dilution in it, by means of the fact that he (or his wife) would experience a reaction to the homeopathic preparation but would not with the container of solvent. It's been ages since I checked out the thread, but the ultimate problem (as I understand it) is that although he was initially 100% certain that this would work, he has tried it out and, well, it doesn't work.
If Vithoulkas would claim (and demonstrate) that he's able to pick out a homeopathic remedy among an array of non-homeopathic preparations at a rate statistically higher than chance, I am sure that the JREF would be VERY interested. But we don't know what his claim is (if there is, in fact, any claim at the moment).
Once again, welcome to the Forum!