In 1988, the multicenter project "Information Network of Departments of Dermatology (IVDK)", including eight university skin hospitals was founded. It now comprises 30 participating centers. At these centers, all patch test results are recorded, together with important anamnestic details and, twice a year, these are sent to the data center at the Göttingen University Skin Hospital. Regular, descriptive analyses of data collected by this epidemiological surveillance system serve the different purposes discussed in this paper: 1) observation of "sentinel events"; e.g. an increase in the proportion of patients tested who were sensitized to a certain allergen, or the identification of certain subgroups at particular risk as a starting point for further research or preventive action, and 2) advancement of good clinical practice in patch testing. In October 1996, a working group of the European Society of Contact Dermatitis (ESCD) called the "European Surveillance System on Contact Allergies (ESSCA)" was established with a similar aim of communal data collection and analysis.