1. Early recognition by clinicians of illnesses suggesting a biological attack is integral to the public health response. 2. The four biological agents of most concern are smallpox virus, botulinum toxin, and anthrax and plague bacteria. 3. Smallpox is distinguishable from chickenpox by the prominent prodromal period and lesions that develop at the same pace and, on any part of the body, appear identical to each other, evolve slowly and are peripherally distributed. 4. The degree of protection conferred by smallpox vaccination given 20 or more years ago is unknown. 5. Foodborne and inhalational botulism could result from deliberate release of toxin. 6. Botulism presents with cranial nerve palsies and descending paralysis in a patient with normal conscious state and no fever.