Portnoy and Barnes. 2003. This review article describes aerobiology of pollen and spores as it relates to human exposure. It reviews a number of studies relating pollen or spore exposure to clinical symptoms or to mediator release. It also reviews controlled exposure vs. natural exposure studies, and provides advice for interpreting pollen counts. The authors feel that the connection between exposure and symptoms is complex and probably varies from person to person and allergen to allergen.