Are you the guy study bioinformatik in FU-Berlin?
Ok, I would suggest your friend get his or her re-entry states visa from canada or Mexico, make sure he or she can re-entry states again after he or she visited you.
Recently it's better do not take risk to come Europe appling re-entry visa back to states, especially those sensitive major. There are already several cases get checking at US-embassy in Berlin, stocklom (One case happened this year in Berlin Max-Plank institue, one chinese guy studies in states was sent by his boss here for cooperation, when he applied re-entry visa to states, he got checking, have to waste several months here.....)
Unless your friend is the citizen of european, otherwise he or she better get visa from Canada or Mexico.
I have several friends came from states to visit me recently, unless those from Japan or States citzen or have canada immigration status, others all get visa in Canada or Mexico.
After Sept. 11, it is a little bit complicated to apply visa via third country.
Good luck! |