The acute responses to cotton dust which characterize the early stages of byssinosis have been reproduced under controlled conditions using bronchial provocation testing with cotton bract extract (CBE). To date this technique has been used primarily as a bioassay to characterize the active component in cotton dust. We report our experience with this technique in two new situations: (1) In the characterization of bronchoalveolar cells and fluid changes resulting from challenge with CBE in healthy naive subjects never before exposed to cotton dust. (2) In the characterization of airway responses in cotton textile workers referred for evaluation of possible byssinosis. This report examines preliminary results in 22 healthy subjects undergoing bronchoscopy following challenges with CBE and 7 workers challenged with CBE. We conclude that bronchoscopy in conjunction with CBE challenge in healthy volunteers is a safe investigative procedure and that CBE challenge in older workers.with lung disease may be helpful in characterizing their disease.