Euxyl K 400 is a preservative for cosmetics and toiletries containing 2 active ingredients, 1,2-dibromo-2,4-dicyanobutan and 2-phenoxyethanol. 2057 consecutive patients with contact dermatitis were patch tested with Euxyl K 400 2.5% pet. and ethanol. A positive patch test occurred in 24 patients (1.2%). The source of sensitization was traced in 8 patients to their cosmetics. Both leave-on and rinse-off products were responsible. Further patch tests with Euxyl K 400 0.5% pet. and phenoxyethanol 5% pet. were performed in 11 patients. A positive patch test to phenoxyethanol was detected in 1 of them. Only 3 patients showed a mild reaction to Euxyl K 400 0.5%. A provocative use test with a lotion preserved with Euxyl K 400 0.1% was positive in 5 of these 11 patients. Patients with Euxyl K 400 sensitivity showed a high prevalence of positive patch tests to other common ingredients of cosmetics. Since the use of Euxyl K 400 in cosmetic products is rapidly increasing, it should be included in the patch test series for patients with suspected cosmetic allergy.