From 1977 to 1983, 12,026 patients were given patch tests with a standard series of substances. A total of 4,494 (37.4%) had positive patch-test reactions to one or more allergens; the average number of positive reactions was 1.85. The most frequent reactions were due to nickel sulphate (positive reactions in 9.2% of those tested), fragrance mix (8.9%), balsam of Peru (6.3%), cobalt chloride (4.7%), potassium dichromate (4.3%) and wool alcohols (4.3%). Women showed significantly more positive reactions than men to nickel sulphate, cobalt chloride, wool alcohols, and parabens and significantly fewer positive reactions than men to potassium dichromate, PPD mix, and epoxy resin. Younger patients showed significant more positive reactions to nickel sulphate and cobalt chloride; middle-aged patients reacted more to potassium dichromate, paraphenylendiamine, formaldehyde and thiuram mix; elderly patients reacted to balsam of Peru, wool alcohols, caine mix, neomycin sulfate, benzocaine, colophony, clioquinol, mafenide, parabens, and gentamycin sulfate.