Hi, I am a post-doc with a J1 VISA, and, as I pay taxes in Italy, I used the Italy-US tax treaty and did not pay taxes for the first two years in the States.
Friends of mine both from Israel and Spain told me that the treaty of US with Israel and Spain, can be extended up to a period of 5 years. From the third to the fifth year they pay taxes but can get a refund afterward.
Is it possible to extend the treaty for up to 5 years also in the case of Italy-US treaty? I was told something about a "trainee" article, but don't know more about this.
If you have information about this I will be grateful.

The exemption is available for 2 years only.

MukatA,
Thank you for your quick answer.
May I ask whether you know if the exemption with Israel is available for 5 years?
Thanks again.

No, it is NOT available. In fact, the Israel-U.S. Tax Treaty is MORE restrictive, not less.