The present work is the first epidemiological study carried out by the Spanish Contact Dermatitis Research Group during 1977. During this year 2806 patients were studied with patch test among 30873 dermatological patients. The 60-62% of the totality had reactivity to one or more patches. Four major groups of allergens were able to consider, following the incidence in their power of sensitize. First group with strong incidence include: Nickel, Chromate, Cobalt, T.M.T.D.,P.P.D.A., Mercapto mix., and Wood tars. Second and third groups with medium incidence contain: Caines, Carbonates, Neomycin, Balsam of Peru, Mercury, Lanolin, Naphtyl mix., Formaldehyde, Benzalkonium chloride, P. P. D. A. mix, and Turpentine. Four group show very low incidence substances, as: Epoxi, Sulfonamides, Etilendiamine, Parabens, Chinoform, Colophony and Cinnamon oil. Few comments about age and occupations are included.