The preservative methyldibromo glutaronitrilc (MDBGN) is used non-occupationally and occupationally. High contact allergy rates have been reported when tested in consecutive dermatitis patients as well as clinical cases with allergic contact dermatitis. Up till now there has been no agreement on which patch test preparation to use to trace contact allergy to MDBGN. From the year 2005 on, MDBGN at 0.5% w/w in petrolatum is recommended for the European standard patch test series. The choice of 0.5% is based on consideration of rates of contact allergy, doubtful and irritant reactions, as well as on information on clinical relevance represented by results of a repeated open application test, and patch test concentrations to diagnose allergic contact dermatitis from MDBGN in individual cases.