We report the patch test results of 449 construction workers who came as patients to the Occupational Dermatology Service of the Instituto Nacional de Medicina y Seguridad del Trabajo in Madrid between 1989 and 1993. 90.8% of them were patch tested, because they had cutaneous lesions or a clinical history suggestive of occupational dermatitis. 65.5% (268) of those patch tested showed one or more reactions connected with their work. Chromate at 42.1% was the main allergen, followed by cobalt, 20.5%, nickel, 10%, and epoxy resin, 7.5%. 25.9% (106) of patients showed sensitization to rubber components, the majority at 23.7% to thiuram mix, with TETD being the main allergen.