BACKGROUND: Baker's asthma is a common occupational respiratory disease and its prevalence rate varies from 15% to 30% of the workers in foreign countries. It has been reported mainly in bakers and millers due to sensitization to wheat, rye, storage mites, and several enzymes etc. But, the main allergen of baker's asthma is wheat. As there is an increase of consumption of food made of wheat due to westernized life style, it is expected that the prevalence of baker's asthma is increasing or already increased. But, there has been no study to investigate the prevalence of baker's asthma in this country. OBJECTIVE: The purpose of this study was to investigate the prevalence of baker's asthma due to wheat sensitization in baking factory workers. METHOD: A total of 147 bakers (age 32.6+/-8.2 years, male 63%) were enrolled in this study. They responded to a modified ISSAC questionnaire and underwent methacholine bronchial challenge test, and skin prick test with common inhalant allergens and work-related allergens including commercial wheat antigen, bread flour, and cake flour antigen prepared in our laboratory. And specific bronchial challenge test with wheat extract was performed to volunteers. RESULTS: The atopic prevalence based on skin prick test was 43% (63/147), and wheat sensitization rate (including commercial wheat, bread flour and cake flour antigen) was 15% (22/147). The risk factors for wheat sensitization were atopy, long duration occupied in baking process, and current or past work history in mixing and/or measuring part where wheat flour exposure was relatively high (p<0.05). Wheat sensitization was highly associated with bronchial hyperresponsiveness, work related symptoms such as asthma, rhinitis, conjunctivitis, and dermatitis (p<0.05) respectively. The prevalence of current asthma based on questionnaire and methacholine bronchial challenge test was 8% (11/147 bakers). Of these, 8 bakers were sensitized to wheat antigen, and all of them except one baker complained of work-related symptoms. These seven bakers were highly suspected of baker's asthma due to wheat sensitization. Two of these seven bakers showed early asthmatic response on specific broncho-provocation test. CONCLUSION: Wheat sensitization rate was 15%, The prevalence of baker's asthma due to wheat sensitization was 5% in baking factory workers and it's risk factors were atopy, long duration occupied in baking process, and current or past work history in mixing and/or measuring part of baking process.