When using patch tests to objectify contact allergy in patients, many different materials are used in different clinics. Whatever the material used, there are presumably differences in the quantities of allergens dispersed in petrolatum applied in the patch tests by the clinicians. Therefore, we designed an experiment in order to evaluate whether such differences do indeed exist. The results presented here clearly show that the quantities of petrolatum applied varies considerably in the patch tests (i.e. Leukotest Beiersdorf) from dermatologist to dermatologist. In addition, we found that for an individual dermatologist differences occur from day to day. It is our conclusion that in the interest of the patients and in the interest of multicentric studies, standardization of patch test materials is of great importance, especially in regards to the quantities of petrolatum applied.