Scientists involved in weapons research are being affected by extra US security checks on visa applications. According to an article in the journal 'Science', scientists from the former Soviet Union and China have been the most heavily affected. Delays have already put back plans to bring together select groups from the former Soviet Union and the United States to discuss how to protect civilian populations from terrorist acts. One recent workshop to discuss detection of toxins and pathogens using bioluminescent alarm signals was postponed from the beginning to the end of August after five scientists failed to obtain US visas Ironically, the new security measures could have negative impacts, making it more difficult for US scientists to benefit from foreign researchers' knowledge of non-proliferation programmes and the protection of civilians from terrorist acts. Routine scientific exchanges appear to be unaffected by the additional security however, with the US National science foundation reporting no drop in collaborations with foreign scientists.