BACKGROUND AND OBJECTIVE: TDI is known to be the most prevalent cause of occupational asthma ( OA ) in Korea. However, the pathogenesis of TDI - induced occupational asthma still remains to be further clarified. So, we evaluated clinical significance of serum specific IgG and IgE antibodies to TDI - HSA conjugate in TDI - induced occupational asthma. Subjects and METHODS: Serum specific IgG and IgE antibodies to TDI - HSA conjugate were measured by enzyme linked immunosorbent assay. Serum was collected from 50 TDI- induced OA patients ( classified as group I ), and was compared with that from 13 asthmatic subjects with negative TDI - bronchoprovocation test ( BPT, group II ), allergic asthmatics ( group III ), and unexposed healthy controls ( group IV ). RESULTS: The prevalence of specific IgG was significantly higher in group I than in group II (p = 0.01) or group III (p <0.01). No significant difference was noted between group II and group III (p> 0.05). However, the prevalence of specific IgE was not different between group I and group II (p> 0.05 ) or group II and group III( p> 0.05 ). There was no significant difference in prevalence of specific IgG according to the asthmatic response during TDI bronchoprovocation test ( p> 0.05 ). No statistical significance was noted between specific IgG and IgE antibodies in group I subjects ( p> 0.05 ). CONCLUSION: These findings demonstrate that presence of specific IgG to TDI - HSA conjugate is closely related to TDI - BPT results and it may contribute to the development of TDI - induced asthma.