Through cooperation between the German Contact Dermatitis Research Group (DKG) and the Information Network of Departments of Dermatology (IVDK), results of standardized patch tests performed by the participating centres are centrally recorded in Germany. For this study, data from 24 departments of dermatology (19678 patients) were evaluated retrospectively and separately for 1995 and 1996. With decreasing frequency, nickel, fragrance mix, balsam of peru, and thimerosal yielded positive reactions most often; surprisingly high numbers of positive reactions were also seen with amerchol L-101 and palladium. Differentiated lists of allergens were compiled for 1995, referring to subgroups of patients (defined by gender, age, localization of eczema, geographical region, occupation, sensitization) and particular problems. In men, percentages of positive reactions were markedly lower for nickel, fragrance mix and balsam of peru than in women. Younger patients reacted more often to thimerosal and older ones to topical medical preparations. Medical allergens were also often positive in patients with leg eczema, whereas occupational allergens were found more frequently in patients with hand eczema. A comparison of positive reactions obtained in distinct geographical regions was problematic because of differences between test populations. The spectrum of allergens found in office workers was similar to that of the whole test population. Patients with positive reactions to nickel and fragrance mix had more positive reactions to unrelated allergens than the total test population. Sex- and age-adjusted frequencies of sensitization revealed a decrease in reactions to nickel and an increase in reactions to mercury allergens from 1995 to 1996. The clinical relevance of mercury reactions was often not apparent. Differentiated lists of allergens can be used to improve the quality of diagnostic and prophylactic procedures in allergic contact dermatitis.