Background: IgE-mediated sensitization of questionable clinical relevance is routinely demonstrated in patients with atopic eczema (AE) by skin prick test or radioallergosorbent test (RAST). We report the results of a randomized, double-blind multicenter study in patients with AE on the relevance and technical aspects of aeroallergen patch testing (atopy patch test, APT). Methods: Two hundred fifty-three adult patients with AE in remission were tested in 7 study centers on clinically uninvolved, unabraded back skin with 3000 to 10,000 PNU/g of Dermatophagoides pteronyssinus, cat dander, grass, birch, and mugwort pollen allergen extracts in petrolatum. After skin prick and RAST and a detailed history on aeroallergen-induced eczema flares was obtained, reading was done at 48 to 72 hours. Results: Previous eczema flares after contact with specific allergens were reported by 10% (mugwort pollen) to 52% (D pteronyssinus) of patients. The percentage of clear-cut positive APT reactions ranged from 44% with D pteronyssinus to 5% with mugwort. Positive skin prick (36% to 65%) and RAST (49% to 75%) results were more frequent. APT results showed significant concordances with history, skin prick, and RAST for D pteronyssinus, cat dander, and grass pollen (P < .001). Optimal test concentrations were 5000 (grass pollen) and 7000 PNU/g (D pteronyssinus , cat dander). The APT had a higher specificity (69% to 92% depending on allergen) with regard to clinical relevance of an allergen compared with skin prick test (44% to 53%) and RAST (42% to 64%). Conclusion: Aeroallergens are able to elicit eczematous skin reactions after epidermal application. The relevance of aeroallergens for AE flares may be evaluated by APT. (J Am Acad Dermatol 1999;40:187-93.)