Ketoprofen, a derivative of aryl propionic acid, is a non-steroid antiphlogistic, used not only for systemic but also for local treatment (Fastum gel, Profenid gel, Ketonal cream). When applying preparations for external use containing ketoprofen undesirable reactions may develop - irritation, phototoxic reactions, contact and photoallergic reactions. During reabsorption haematogenic reac - tions may develop which have the clinical appearance of drug exanthema. When contact hypersen- sitivity to the effective substance - ketoprofen develops, group hypersensitivity to other aryl propionic acid derivatives may develop, such as ibuprofen, naproxen, alminoprofen, fenoprofen, flurbiprofen and thiaprofenic acid and compounds containing a molecule of benzophenon (e.g. phenofibrate). Undesirable effects which develop after the application of external preparations containing ketoprofen may be also due to other constituents e.g. lavender oil, neroli oil. The authors examined and treated in the course of the year during spring and summer at the First Dermatovenereological Clinic in Brno 10 patients (8 women, 2 men) who used Fastum gel (7x) or Profenid gel (3x) and who developed after application of these external preparations undesirable reactions: 1x dermatitis phototoxica, 1x dermatitis irritativa and seven patients developed contact eczema, incl. one photocontact eczema. Ketoprofen was the allergen proper only in one patient, ketoprofen and lavender oil in four patients, lavender oil only in two, and lavender oil and neroli oil in one patient. Group hypersensitivity to phenofibrate was found five times, to bezophenon, thiap- rofenic acid and flurbiprofen in 3 patients.

        Key words: Fastum gel - Profenid gel - eczema contactum - ketoprofen - volatile oils