Patch testing has rapidly become an important clinical allergy tool, but is underutilized in the evaluation of complex patients, especially when these patients have skin disorders and respiratory allergies, food allergies, or eosinophilic enteritis. Learning when and how to use patch tests thus adds to any practitioner's diagnostic abilities.This review discusses selected studies from the past year, grouped into immunology, pediatric testing, contact allergy, food allergy, and drug allergy.Patch tests can detect a wide range of sensitivities to inorganic and organic chemicals, drugs, biologic molecules, inhalants acting as contactants, food allergens, allergens that have not been commercially extracted, and solid allergens. Because patch tests detect the full range of immunologic reactions, Gell and Coombs type I to IV, they may be uniquely reactive when other allergy tests are negative. Because of the large number of published studies that utilize patch testing, clinicians often can use a literature search of prior studies of similar problems, or for particular allergens, to choose technical details that make successful patch testing more likely.