Clostridiopeptidase A, also called collagenase 1, is a proteolytic enzyme capable of digesting collagen. Preparations containing clostridiopeptidase A are used topically for the debridement of dermal ulcers, burns and other necrotic lesions to facilitate the formation of granulation tissue and subsequent epithelization. We observed 4 patients with a periulcerative eczema after repeated applications of Noruxol ointment (Smith & Nephew Ltd, L Hull, UK). Patch testing with Noruxol ointment as is and its excipients (soft paraffin and white petrolatum), as well as scaled dilutions of the main ingredient of this topical preparation, clostridiopeptidase A (Firma, Florence, Italy), showed doubtful reactions to Noruxol ointment in 3 patients and a positive reactions only in 1 patient. All patients showed positive reactions to clostridiopeptidase A 1% in pet. This study shows the sensitizing capacity of clostridiopeptidase A that should be tested in all patients with suspect sensitization to Noruxol ointment.