In the period from August, 1969, to December, 1970, 27 patients with a contact allergy to Hirudoid ointment have been seen. In 17 of these patients, it could be demonstrated, that this allergy was due to the presence of the preservative CA 24, containing chloracetamide. Therefore, the use of chloracetamide in creams and ointments for medical use has to be omitted.