Workers who process raw silk are exposed to a fine dust derived from the gum that binds the strands secreted by the silkworm. Fifty-three such workers, all women and non-smokers with an average of 5.8 years of service in the industry, were examined. Eighteen (33.9 per cent) workers had occupational asthma, the highest proportion (48.2 per cent) being in those twisting silk. A lower prevalence (20.0 per cent) was found in workers in the degumming sector, while the least (16.6 per cent) was in weavers. This declining prevalence in the three processing stages appears to be in line with their declining exposure to dust. The occupational asthma was of the intermediate and late types occurring 30 minutes to 6 hours after starting work and subsiding 1 to 8 hours after leaving the factory.