In an effort to evaluate conformity with published guidelines for diagnostic allergy skin testing in their locality, a committee of members of the Orange County (California) Society of Allergy and Clinical Immunology surveyed their membership for the number, identity, and rates of sensitization of aeroallergens in a selected patient population. Test data were analyzed on patients who were judged appropriate to undergo immunotherapy. Complete test results of 271 patients were obtained from one third of local allergy specialists. A total of 115 different aeroallergen extracts were identified. By category, tree pollen allergens (32) were followed in declining order by weed pollens (28), molds (22), environmentals (18), and grass pollen extracts (15), for the total of 115. The average number of aeroallergens used by a practice in a comprehensive evaluation was 77 (range, 47-114). When only unequivocally positive reactions were considered (3+ equivalent or greater), Bermuda grass pollen extracts elicited the highest rate, 85%, and the environmental, rat dander, was the lowest at 1.8%. At least 20% of the patients reacted strongly on skin tests to 97% of the extracts. The disparity between the recommendations of a maximum of 30 aeroallergens for a comprehensive evaluation and actual practice procedures merits efforts at resolution.