With the aid of patch tests an investigation involving 3060 patients was carried out to register the incidence and prevalence of allergens of the standard and supplementary test series. The standard series with 16 allergens was selected in cooperation with the work group for curtailing contact dermatitis and occupational dermatoses in the socialist countries. The Czechoslovakian supplementary test series included three allergens: neomycin sulfate, extr . chamomillae and resorcinol. In 22.6% of the 693 patients the skin tests were positive for at least one allergen. The most frequent eczematogenic among men was potassium dichromate (resulting from contact with cement), among women nickel sulfate, and in the group as a whole Peruvian balm. The age groups most affected were between 41 and 50 years and between 51 and 60 years, respectively, for men, between 21 and 30 years for women, and between 21 and 30 years for the group as a whole. In registering the prevalence, chamomillae extract caused the highest occurrence among men, cobalt nitrate among the women, and also cobalt nitrate for the group as a whole. The age group affected most was between 51 and 60 years. In the complete investigative study of incidence and prevalence, Peruvian balm topped the list for the group as a whole, potassium dichromate for the men, and nickel sulfate for the women. Among the men and for the group as a whole the most affected age group was between 51 and 60 years, and among the women between 21 and 30 years.(ABSTRACT TRUNCATED AT 250 WORDS)