The authors have carried out a statistical analysis of cases of occupational asthma and other occupational lung diseases submitted to the Ministry of Labour in Quebec between 1986 and 1988. The total number of claims was 913, 993, and 866 respectively for the 3 years of which 61% to 71% were accepted. 41% to 55% were new assessments. Of 228 new claims accepted in 1988, 81 (36%) were for occupational asthma. This number surpassed the number of claims accepted for traditional pneumoconiosis (asbestos = 30, and silicose = 36). Isocyanates were the principle cause of occupational asthma (23% of cases were recognised in 1988) followed by flour, red and white cedar, snow crab process workers, and various pharmaceutical products and grains. In comparison with statistics in 1977, one noticed there was a large reversal of the frequency of certain occupational lung diseases that are recognised, because at that time asbestosis and silicosis were the principle causes of claims put forward and accepted. The authors discuss the statistical bias of occupational lung disease obtained by medico-legal agencies. Although occupational asthma has not been the object of the systematic screening program in the work place and although there is a tendency for workers to avoid or abandon their occupation more often than in the traditional pneumoconioses current protection is sufficient in Quebec to motivate individuals who are possibly suffering from occupational asthma to put in a claim for compensation.