We studied the association of nonspecific bronchial hyperresponsiveness with general characteristics, exposure concentration, respiratory symptoms, chest x-ray findings, past histories and pulmonary function. We determined bronchial hyperresponsiveness by methacholine challenge test. And we conducted a respiratory symptom questionnaire and performed spirometry on 111 workers occupationally exposed to isocyanates in various industries. About 21.6% of subjects had bronchial hyperresponsiveness. No significant differences were observed between the hyperresponsive and non-responsive group with respect to age, sex, employment period, height, and smoking histories. Cough and breathlessness were significantly associated with the bronchial hyperresponsiveness. The hyperresponsive group had more experience of bronchitis and asthma in the past than the non-responsive group. The lower $FEV_1;and;FEV_1%$ were closely related with bronchial hyperresponsiveness. Bronchial hyperresponsiveness seems to be associated with some of respiratory symptoms, past histories and pulmonary function parameters in workers exposed to isocyanates.