Asthma is the most common chronic respiratory disease among children worldwide. This project investigates the morphological, molecular, and immunological diversity of small-spored Alternaria species associated with the onset of childhood asthma in and around the vicinity of Tucson , AZ. Specific objectives are 1) to obtain a collection of small-spored Alternaria species representative of the species diversity found in the Tucson area, and examine the diversity of recovered isolates using morphological and DNA characteristics; 2) to determine allergen content of recovered isolates using immunological and molecular techniques; and 3) to compare the sensitivity of asthmatic children to allergens extracted from Alternaria isolates collected in the survey, type A. alternata isolates, and isolates used in commercial allergen preparation. If data support these hypotheses, then the potential for commercial development of improved Alternaria allergen preparations for use in standardized allergen sensitization tests is suggested and would be evaluated in future studies.