In 1996, the French Society of Occupational Medicine (SFMT) and the French-Speaking Society of Pulmonology (SPLF) established the National Observatory of Occupational Asthma (Onap). Based on a national network of volunteer physicians, its purpose was to collect cases of occupational asthma (OA). However, several methodological criticisms could be raised regarding the use of these data for epidemiological surveillance purposes: - the voluntary nature of the system leads to an underestimation of the actual number of OAS cases and a lack of information on the source population from which these cases originate, making it difficult to estimate incidence rates; - the absence of diagnostic criteria for identifying cases of OA. In light of this, a new study was proposed by the French Institute for Public Health Surveillance (InVS) to the SPLF and the SFMT: the Onap II project. (R.A.)