A worker who ground the inner parts of camshafts for automobile engines using water-soluble metalworking fluid (MWF) for 14 yr was diagnosed with sinusitis. We postulated that the cause of sinusitis might be associated with exposure to microbes contaminating the water-soluble MWF used in the grinding operation. To uncover responsible agents for this case of sinusitis, a quantitative exposure assessment for chemical and biological agents was made and prevalence of work-related respiratory symptoms was investigated by questionnaire. The exposure ranges of MWF mist (0.59 mg/m(3) to 2.12 mg/m(3)) measured during grinding exceeded 0.5 mg/m(3) of the recommended exposure limit (REL). Grinders' exposures to bacteria, fungi and endotoxins were also generally higher than not only the proposed standards, but also those reported by several studies investigating the causes of respiratory effects. Statistical tests indicated that the prevalence rate of reported symptoms related to nasal cavities showed no significant differences among the operations. Evaluation of grinding operation characteristics and the quantitative exposure assessment indicated that repeated exposure to MWF mist, including water-soluble MWF contaminated with microbes may cause respiratory diseases like sinusitis or at least increase susceptibility to the development of sinusitis. Further study is underway to identify environmental risk factors for sinusitis by analyzing the relationship between medical examination results and plant characteristics including exposure data.