We describe a case of a 40-year-old non-atopic woman with recurrent leg ulcers because of the factor V Leiden mutation who developed a severe eczematous lesions of the skin surrounding an ulcer of the right leg after the use of a protease-modulating matrix (Promogran, Johnson and Johnson, Gargrave, Skipton, UK). The patient was patch tested with the SIDAPA (Italian Society of Allergological, Occupational and Environmental Dermatology) standard series, a piece of the device as is, of the bovine collagen (Zyderm, Collagen Corporation, Palo Alto, CA, USA) as is, a piece of the gauze containing only regenerated oxidized cellulose (Tabotamp, Johnson and Johnson, Gargrave, North Yorkshire, UK) and of a fold towels in pure cellulose (Foscart, Bassano del Grappa, Italy). Patch tests gave a positive reactions to nickel sulphate and Promogran as is. We showed that the sensitizing agent was regenerated oxidized cellulose, a substance the treatment of ulcers and as is in and in combination with collagen in surgery for intraoperative hemostasis. The case reported suggests that regenerated oxidized cellulose can cause allergic contact dermatitis.