The study examines the degree of bronchial reactivity among subjects who had asthma during work at a cotton mill and with no previous history. Ten subjects were included, 9 smokers and 1 non-smoker. Mean age 26.3 years mean employment time 15.7 months, mean debut of symptoms 5.6 months. Because of asthmatic symptoms all had been withdrawn from the cotton mills more than 2 months previous to this study. All subjects had no longer symptoms and lung function tests did not show any degree of bronchoconstriction. The Following tests were made: Standard and cotton skin-prick, eosinophile count, RAST(Cotton, Bracts, Storage mites and A.Fumigatus), precipitins to Wards moulds, lung function total IgE and Histamine PC20. All subjects had a degree of hyperreactivity with a mean PC20 of 1.60 mg/ml. Only one subject shoved a positive RAST towards green bract. The other results did not show any significance. We conclude that the working environment in cotton mills produce a non allergic bronchial hyperreactivity leading to symptomatic asthma. This could be due to the high levels of endotaxins in cotton mills, as we Found a normal IgE in 80% of the subjects.