The results of the immediate skin test response to a panel of 16 common aeroallergens performed in a group of 659 consecutive patients with symptoms suggestive of a respiratory allergy were analyzed. A group of 108 healthy individuals served as control subjects. Ninety-four percent of the patients and 87% of the control subjects had at least one allergen-induced reaction (wheal ≥2 by 2 mm). The prevalence of positive skin reactions to each aeroallergen was equally high in both groups. However, if a skin reaction is considered as positive only when an allergen-induced wheal is equal or larger compared to the 50% of the wheal obtained with the histamine control in that individual, 70% of the patients had positive skin reactions and only 38% of the control subjects were positive (p < 0.05). Similarly, the prevalence rates to five aeroallergens (pollen, Fusarium, Mucor, Pullularia, and Curvularia) in the patient group were reduced to those levels observed with the control group, suggesting they are clinically less important. The age and not the sex influenced both the prevalence rates (p < 0.001) and the mean size (p < 0.01) of allergen and histamine-induced skin reactions. Lower prevalence rates and mean size values were observed in the youngest group (0 to 9 years). Moreover, there was an inverse relationship between lower skin reactivity with more younger subjects in our patient population. These results indicate that patients and healthy individuals have similar mechanisms for skin reactivity. The size of the allergen-induced wheal reaction compared to the histamine-induced control wheal reaction appears to be an important consideration for the correct clinical interpretation of the results. The observation that there were more younger patients with lower skin reactivity suggests that other mechanisms not detected by skin testing may play a role in the pathogenesis of respiratory allergies. © 1988.