We report a patient with an allergy induced by photodynamic therapy (PDT) following simultaneous treatment with both 5-aminolaevulinic acid (ALA) and ALA methylester (ALA-ME). After several PDT treatments the patient presented with acute eczema of the treated areas and itch and hyper-reactivity of the untreated skin. Patch testing demonstrated a strong +++ reaction to ALA-ME only, indicating that derivatives common to ALA and ALA-ME were not involved. This is the first case of allergy to ALA-ME.