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Britain’s Health and Safety Executive has finally classified tissue from the nervous systems of cows infected with BSE as a dangerous biological agent, following evidence linking it to the new variant of Creutzfeldt-Jakob disease (This Week, 4 October, p 6). Researchers must now handle the material in a microbiological safety cabinet in a separate room. Although the agent had previously been classified as harmless to people, these precautions were already routine.