Abstract Background: Patch testing with dust mite antigens might identify mite-sensitive individuals, particularly those with atopic dermatitis who can benefit from avoidance measures. Currently available dust mite allergens have not been well studied. Objective: To determine the proper dilution of 20% Dermatophagoides pteronyssinus/farinae mix antigen (Chemotechnique, Malmo, Sweden) for use in closed patch testing. Methods: Eighteen nonatopic, healthy control subjects were patch-tested to the 20% concentration, yielding 15 (83%) positive reactions, most showing a decrescendo or persistent pattern suggesting an inordinately high number of false positive reactions. Dilutions of 1.25% to 0.1% in white petrolatum were used in patch testing 8 atopic dermatitis and 11 respiratory atopy patients, and 12 nonatopic controls. Results: Positive reaction rates to the 0.25% and 0.1% concentrations, respectively, were 87.5% and 62.5% for atopic dermatitis, 54% and 18% for respiratory atopy, and 33% and 8% for healthy controls. Using Fisher's exact test, the 0.1% diliution was shown to significantly differentiate rates of positivity among the 3 groups, particularly between atopic dermatitis subjects and healthy controls. Conclusion: We find that a 0.1% dilution of 20% D. pteronyssinus/farinae mix antigen (Chemotechnique) to be useful in identifying mite-allergic individuals with atopic dermatitis.