Asthma from exposure to inhalation of isocyanates is an affection recognised under the title of work place diseases within table no 62 in the General Regulations and no 43 in the Agricultural Regulations. If workplace induced asthma is the most frequent of the workplace respiratory illnesses with a frequency of 2 to 15% of the asthmatic population, 1 patient in 2 will only be the object of a declaration and 1 in 3 the objective of a survey by the administrative authorities. The frequency of isocyanate asthma is on average 16.4% amongst workplace asthmas (19.6% in the industrial environment and 1.5% in an agricultural environment); if this prevalence is dose-dependent according to Baür, 30% of patients exposed to weak doses of isocyanate (0.3% ppb according to White) develop asthmatic disease whilst Bernstein estimates as 5 to 10% the frequency of asthmatic disease per 100,000 persons who are exposed to isocyanates.