Events following the anthrax letter incidences in 2001 changed many previously held assumptions regarding biological aerosol hazards. As there were significant fatalities resulting from the sorting of a single anthrax letter, it suggests there is a need to reevaluate how best to measure biological aerosols and to use the information to make accurate predictions. This paper describes the biological aerosol created from manipulating envelopes containing Bacillus subtilis globigii spores (a simulant for anthrax). In addition, the measurements on dispersion of spores from an envelope processed by a mail sorter provide important dynamic aerosol characteristics, information previously unavailable for health risk assessment. The findings produced a number of significant aerosol dosage estimates related to spore contaminated letters. Graphic presentations show significant hazard in handling anthrax-laced letters. Aerosol particle dynamics are described and specific lethal dosage values are listed for a range of activities; these will be useful in assisting the modeling community to create more realistic predictions in hazard assessment studies. Crown Copyright (c) 2005 Published by Elsevier Ltd. All rights reserved.