From the University of Louisville, Division of Dermatology. Presented at the American Contact Dermatitis Society Annual Meeting, San Francisco, Calif., March 19, 1997. Accepted for publication Feb. 22, 1998. Reprint requests: Joseph F. Fowler, MD, University of Louisville, Division of Dermatology, Department of Medicine, 310 E. Broadway, Louisville, KY 40202. Copyright © 1998 by the American Academy of Dermatology, Inc. 0190-9622/98/$5.00 + 0 16/1/89785 Methyldibromoglutaronitrile (MDGN), also called Tektamer 38 (Merck & Co., Rahway, N.J.), is a component of some skin care products. It is combined with phenoxyethanol in a 1:4 ratio to make Euxyl K400, which is used as a preservative in cosmetics and toiletries.1 Euxyl K400 was developed as an alternative to the mixture of methylchloroisothiazolinone and methylisothiazolinone (MCI/MI), also called Euxyl K100 and Kathon CG (both manufactured by Rohm & Haas, Philadelphia, Pa.) which was causing a significant amount of cosmetic allergy in Europe.2,3 Euxyl K400 has been used as a preservative in Europe for many years; however, its use in the United States is more recent. MDGN is the sensitizing agent of Euxyl K400 for most patients, because contact allergy to phenoxyethanol is rare. Euxyl K400 (specifically MDGN) is being found more frequently as the cause of contact dermatitis in Europe. Because its use in the United States is more recent, MDGN’s reported frequency of contact sensitivity in the United States is much lower.1 The prevalence reported by the North American Contact Dermatitis Group (NACDG) from 1992 to 1994 was 1.5%.4 We found a positive patch test to MDGN in some consecutively tested patients that was relevant to their dermatitis and the products that they were using. We therefore performed a review of patients who were undergoing routine patch testing to determine the prevalence and relevance of positive reactions to MDGN.