We have reviewed a number of aeroallergens, derived from arthropods, that can induce allergic respiratory illnesses. The insects and acarids responsible often are easily overlooked or, if evident, have allergenic impacts that are not well recognized. Use of techniques such as RAST, RAST inhibition, and assays of mediators from both passively sensitized lung and basophil-rich leukocyte suspensions has facilitated identification of these new allergens and their sources. Direct skin and inhalation challenge testing have provided clinical correlations in vivo, emphasizing the potential importance of these agents. The high prevalence and intensity of type 1 responses to environmental arthropods (eg, cockroaches, house dust mites, moths, and butterflies) suggests that their significance as causes of persistent airway diseases may, at times, exceed that of pollens. Further investigation clearly is warranted, and it is our opinion that arthropod allergies must be considered and investigated seriously in all patients with respiratory allergy that is not otherwise readily explained, particularly bronchial asthma. Such an enlightened approach offers both a fuller understanding of disease causation and, we believe, a means to achieve improved patient care.