Evidence for the effectiveness of patch testing and the need for an expanded series that provides experience and evidence-based suggestions for an extended patch testing series are examined in this review. Many of those testing with shorter allergen series are interested in expanding the spectrum of patch testing. The American Contact Dermatitis Society (ACDS) Core Allergen Series Group has arranged a group of suggested allergen groups that can be logically scaled up or down depending on the needs of the patch tester and the community being tested. This is not an "ACDS 80 Standard". We suggest a core group of allergens similar to the TRUE Test (SmartPractice, Phoenix, Ariz) with subsequent trays providing a greater breadth of coverage in a logical fashion, with more likely allergens being higher in the tray. For more extensive testing, specialty trays (ie, cosmetics, metals, plant, etc) are recommended.