A study of respiratory symptoms and dust exposures in the English wool textile industry was conducted. The cohort consisted of 2783 workers employed at 15 wool textile mills in the west Yorkshire area, United Kingdom. The subjects completed a respiratory symptom questionnaire. Personal air sampling for respirable dusts was performed. Endotoxin concentrations in some of the samples were determined. Respirable dust concentrations ranged to over 100mg/m3. At least 9% of the subjects were exposed to average overshift dust concentrations of more than 10mg/m3. Wool opening, blending, worsted carding, and carpet yarn backwinding were very dusty jobs, being associated with average dust concentrations of 14.8, 180.5, 39.1, and 46.7mg/m3, respectively. Endotoxin concentrations ranged up to 650 nanograms per milligram. Chronic bronchitis, wheeze, grade 3 dyspnea, persistent rhinitis, conjunctivitis, chills, and ten or more nosebleeds in the past year were the most frequently reported symptoms. The prevalences of chronic bronchitis, wheeze, dyspnea, persistent rhinitis, and conjunctivitis were significantly associated with current dust exposures after adjusting for age, sex, smoking, and ethnicity. Logistic regression analysis predicted a rapid increase in respiratory symptoms for respirable dust exposures up to 5mg/m3 and a slower increase for dust concentrations of 5 to 20mg/m3. The highest risks were for female European employees. The relative risks for rhinitis, chronic bronchitis, conjunctivitis, and grade 3 dyspnea due to respirable dust concentrations of 10mg/m3 relative to nonsmoking women 40 years of age were 2.47, 2.77, 3.56, and 6.20, respectively. The risk for taking sick leave increased with increasing dust exposure. The authors conclude that exposure to wool mill dust at concentrations comparable to those of nuisance dust, up to 10mg/m3, can cause respiratory symptoms.