The combination of methyldibromoglutaronitrile (MDBGN) and phenoxyethanol (PE) is widely used as a preservative in body care products. Sensitization rates to MDBGN have increased parallel to its increasing use in cosmetics, skin care products, and moist toilet paper since the early 1990s, whereas PE is obviously not a sensitizer. The optimum patch preparation for diagnosing a contact allergy to MDBGN is still a matter of debate.This study was performed to assess an adequate patch test concentration for MDBGN/PE and MDBGN.Based on previous results from other countries, the German Contact Dermatitis Research Group (DKG) performed parallel patch tests with MDBGN/PE 0.5% in petrolatum (pet.) and 1% pet. in 4,615 patients and with MDBGN 0.1% pet. and 0.3% pet. in 988 patients. The results of these tests, performed in routine patch testing, were collected and analyzed be the Information Network of Departments of Dermatology (IVDK).Comparing MDBGN/PE 0.5% pet. with 1.0% pet., the percentage of patients showing a positive test reaction increased from 2.3% to 3. 5% (P <.001), mainly because of an increase in weak positive reactions. The reaction index remained stable at 0.54. Comparing MDBGN 0.1% pet. with 0.3% pet., the percentage of patients with positive reactions increased from 1.4% to 3.3% (P <.001), and the reaction index decreased from 0.33 to -0.10. With the lower test concentration, 79% of the positive reactions were only +, with the greater concentration, this was true of 64%.Testing MDBGN/PE 1.0% pet. shows additional cases of contact allergy to MDBGN that would have remained undetected with MDBGN 0.5% pet. The greater test concentration seems to have no disadvantages in quality. The DKG decided to keep MDBGN/PE 1.0% pet. in the standard series. MDBGN 0.3% pet. leads to far more doubtful or irritant test reactions than MDBGN 0.1% and may produce false-positive patch test results. Therefore, the DKG recommends testing MDBGN 0.3% pet only in special cases.