In October, SciDev.Net provided a link to a news article in Nature, which said that scientists from 'countries of concern' might need to obtain a licence to work with US laboratory equipment (see Foreign scientists may need special US licence).
Writing to Nature in response to the original news item, Peter Lichtenbaum, assistant secretary for export administration at the US Department of Commerce, says that in fact the licenses would be required for the transfer of skills, not the use of equipment.
Lichtenbaum adds that, contrary to what was said in the original Nature news item, researchers have never been exempt to the transfer rules. He provides a link for further information on the Department of Commerce website.
Reference: Nature 432, 15 (2004)