I am a visiting professor from Hungary. I was in the USA working as a postddoc at UNC Chapel Hill from 2002-2005. During this period I was tax exempt based on the Treaty Article 17 for 2 years. Then I returned to Hungary for the next 5 years, and in 2010 I did a short research program (50 days), same institution, as a visiting professor, also with a J1 visa. Can I claim again the tax treaty benefits for this income?

No, you do not get treaty benefit again.

This is what I thought, by the way. However, there is clear statements in other treaties (e.g. the Slovak one) which says that treaty benefits can be used only once in a lifetime. Thus, theoretically, there must be an option or condition or treaty when using the treaty benefits a subsequent time is available, isn't it? The Hungarian doesn't clearly restrict that. So, theoretically using the benefits multiple times is not a violation of the tax treaty. This is not clear from the actual text of the treaty.

@arapd17:
There is a rule called the 6 year look back rule. You cannot get another exemption, if you were exempt 2 out of the last 6 years.