In 1991, only a low frequency (0.5%) of sensitization by the newly introduced preservative 1,2-dibromo-2,4-dicyanobutane (synonym: methyldibromoglutaronitrile; trade names: Euxyl K400, Merquat 2200, Tektamer 38) was encountered in the Netherlands. It has subsequently been increasingly used in our country as a preservative in moistened toilet tissues, and also in cosmetics such as body milk, lotions and creams. This prompted us to re-evaluate the frequency of sensitization. From January 1993 until July 1994, all consecutive patients attending for routine patch testing were also tested with 1,2-dibromo-2,4-dicyanobutane (0.1% petrolatum): one of 281 (0.3%), nine of 281 (3.2%) and six of 247 (2.4%) were found to be positive in the first and second halves of 1993 and the first half of 1994, respectively. In at least 12 of 16 patients this allergy was responsible for their presenting complaint (perianal and facial dermatitis). As 12 of 16 patients had intensively used moistened toilet tissues containing this preservative, this habit is presumably the cause of sensitization. Our data indicate that the frequency of sensitization is approaching that of allergy to methyl(chloro)isothiazolinone (Kathon CG; 1993: 2.3% in our hospital), a well-known allergen, which seems to have been partially replaced in cosmetics and toiletries by this new preservative.