79 cotton workers with a variety of work related respiratory symptoms and 84 matched asymptomatic workers underwent histamine challenge testing (Yan method) and skin testing to investigate any relationship between bronchial hyperreactivity, atopic status and symptoms. 23 of the symptomatic group were byssinotic. 18/23 byssinotics, 21/56 non byssinotic symptomatics and 14/84 controls had evidence of bronchial hyperreactivity. Byssinotics had a significantly lower PD(20) than the other operatives. The prevalence of atopy was equal in the three groups. This study documents the presence of bronchial hyperreactivity in the majority of cotton workers with byssinosis.