Organic photopolymerizable resins increasingly used in printing make it possible to produce flexible, lighter plates. A certain number of skin lesions and general symptoms appeared upon manipulation of plates made by the Letterflex process. In the workshop where this study was carried out, 12 out of 15 people suffered various degrees of skin lesions. The epicutaneous tests and biopsies performed indicate an allergic type reaction to one of the resin's constituents, polythiol. Experiments with animals confirm the strong allergenicity of this compound.