A standard patch test series was tested for 7 years (1977-1983) in a total of 11,962 patients. The annual frequency of positive reactions to the compounds tested was assessed for the total and for males and females separately. During the observation period, there were significant increases in positive reactions in the total group from 6.2% to 12.7% for nickel sulphate, from 5.3% to 7.0% for balsam of Peru and from 3.8% to 6.5% for potassium dichromate, reflecting significant changes in both sexes. The frequency of positive reactions to wool alcohols, formaldehyde, neomycin sulphate, paraben mix and gentamycin sulphate significantly increased, while that of positive reactions to clioquinol, mercuric chloride and turpentine peroxide significantly decreased in either males or females, sometimes leading to significant changes in the total group.