Polyfunctional aziridine (PFA) is increasingly used as a water-based crosslinker in two-component paints, paint primers, lacquers, topcoats and other protective coatings. The crosslinker is made by reacting multifunctional acrylic monomer with a highly reactive aziridine compound. Respiratory allergy or hypersensitivity from PFA has not been reported previously. During 1978–1991 we came across nine cases with hypersensitivity from PFA: two had allergic contact dermatitis (ACD), four had occupational asthma and three had both of them. Five of the patients were parquet layers, two were fibre-board painters, one was a spray painter and one was a salesman of PFA products, ACD was diagnosed by positive allergic patch test reactions with PFA in a dilution series in petrolatum: 0.32%-0.5% gave a 2+-3+ allergic reaction in the five cases with ACD but 0.1% gave only a weak reaction in one case, whereas the methacrylale patch test series was negative. The diagnosis of seven cases of occupational asthma due to PFA hardener was based on symptoms related to exposure to PFA hardener at work, and on positive provocation tests with PFA hardener. One had an immediate type reaction, one a dual reaction, and the others had late reactions. The positive reactions with the PFA hardener and the negative reactions with the acrylate compounds indicate that PFA caused ACD which is different from the previous reports in which acrylates present as impurities in the PFA hardener caused the sensitization. Patch testing with 0.5% PFA hardener should be performed in patients with contact dermatitis if exposure to PFA has occurred. PFA hardener may also cause occupational asthma. The cause-effect relationship can be verified with chamber challenge tests. The mechanism of the asthmatic reaction is obscure as with many other low molecular weight chemicals. The exposure to PFA hardener should be minimized at the workplaces to prevent sensitization. Careful protection of both the skin and the respiratory tract is mandatory.