To evaluate the significance of specific IgG and specific IgG4 in the development of work-related respiratory symptoms, specific IgG and specific IgG4 to Black GR-human serum albumin (HSA) conjugate were measured by ELISA in 309 dye-exposed workers and 63 unexposed patients as negative controls. A survey revealed that 78 (25.2%) had work-related lower respiratory symptoms with or without nasal, skin or eye symptoms. Specific IgG and specific IgG4 were detected in 23% and 14% of the exposed workers, respectively. The prevalence of specific IgG and specific IgG4 was significantly higher in smokers and workers with specific IgE or those with lower respiratory symptoms (P less than 0.05), but was not associated with work station, duration of dye exposure or atopy. These results suggested that the existence of specific IgG to Black GR-HSA might represent a response to Black GR exposure and be closely related with work-related respiratory symptoms.