Hello,
I am an Italian citizen and I will be hired as a post-doc in US with a J-1 visa beginning of February 2011.
Two years ago I was already in US for 5 months under J-1 visa but I did not receive any salary for that (it was an internship during my PhD).
My question is: the 2 years period of tax exemption will start with the second J-visa (so from 2011) or it is already expired even if I never ask for tax return as I never earn money in US?
Thanks!

There is a problem with the IRS website that has the latest U.S.-Italy Tax Treaty, so I could not check the treaty.

However, I do not think the previous J-1 visit will affect your exempt status, provided you qualify to begin with. I say this because it is my experience that post-doc positions do NOT qualify for the tax exemption; they are treated as student visas.

Thank you very much!
I am pretty sure post-doc can qualify for the tax exemption as some of my Italian friends doing post-doc in US can do this. I was just worried about my previous visa. Where can I found more information about that?