Component-resolved diagnosis of allergies allows disease-specific patterns of sensitization in some conditions such as allergic bronchopulmonary aspergillosis ABPA). By determination of IgE against important pollen allergens such as Bet v 1, Ole e 1 or Phl p1/Phl p 5, more precise guidance for allergen-specific immunotherapy may be achieved, as pollen extracts contain mostly these major allergens. Sensitizations against minor allergens such as profilins or polcalcins influence the outcome of IgE measurements against full allergen sources, but are often of limited clinical relevance. In food allergy, frequent cross reactivity between pollens such as birch pollen via Bet v 1/PR10 proteins can be identified. Sensitization against some storage proteins such as peanut (Ara h 2) or lipid transfer proteins of peach (Pru p 3) or hazelnut (Cor a 8) may indicate an increased risk of severe anaphylactic reactions. Exercise-induced anaphylaxis, unclear sensitizations against latex or double-positivity in insect allergy are other useful indications for component-resolved diagnosis. Microarray-based allergen chip diagnosis makes possible today the detection of IgE against more than 100 allergens in tiny amounts of serum and is very promising, but still needs evaluation and optimization in regard to allergen selection and sensitivity.