 Visit 3: Oral graded ASA challenge will be performed to confirm or rule out the presence of ASA-hypersensitivity. This visit will take place at least 1 week after Visit 2. Both groups will undergo an oral graded ASA challenge as per earlier described protocol. Urine and plasma will be collected from the patients at several time points. Hypersensitivity reactions will be defined in four different ways: a decline in forced expiratory volume in 1 second FEV1 of at least 15 combined and naso-ocular reaction; b 20 decline in FEV1; c isolated naso-ocular reactions; d isolated cutaneous reactions hives and swelling. Patients with reactions will be treated according to their symptoms. 