In this investigation the notion 'specificity' of the test method also used by the Nickel Test Sensitive is defined as follows: Specificity is defined as the number of true negative test results divided by (the number of true negative + the number of false positive test results). True negative reactions were defined as 'negative DMG-test reactions confirmed by a nickel release below 0.5 μg nickel . cm-2 . week-1. False positive test results were defined as 'positive DMG-test reactions but with a nickel release below 0.5 μg nickel . cm -2 . week-1'. Thus, the true prevalence of materials that release too much nickel will be underestimated if one only relies on positive DMG test results.