Isocyanates, which are used in many industrial processes, are known as being respiratory irritants and sensitizers, with asthma being one of the most serious manifestations. For several years now, the method of diagnosing occupational asthma caused by diphenylmethane diisocyanate (MDI) consists of exposing workers to this substance in the laboratory in solid form, which is heated. The aim of this study is to verify whether MDI is then effectively present and to determine the other compounds generated in order to establish objectively and ultimately the products responsible for this asthma. With this study, the current MDI generation technique or new techniques can be validated and methods for sampling the other compounds emitted can be developed.