All contact dermatitis patients are told to avoid their specific allergens. As regards topical pharmaceutical agents, however, it is almost impossible for these patients to identify the products that contain their allergens. In order to provide reliable information for these patients, we have designed a computer assisted data system. The CODEX (COntact DErmatitis indeX) system consists of three computer readable files: a Product File containing the complete composition of the pharmaceutical products on the Belgian market that are applied on the skin and the mucous membranes, a Patient File with the patient's anamnesis, and a Literature File with cross-referenced material on contact dermatitis. Each patient is given a list of the products that contain his/her allergen(s). The data bases are analyzed statistically and updated periodically. Cosmetics in general are excluded.