This study was undertaken to assess the change in spirometric parameters (FEV(1), FVC), and bronchial reactivity (BR) using the Yan Method across working shifts at the beginning and end of the working week. Four groups of operatives were identified; 1) operatives with symptoms of byssinosis 2) operatives with work-related respiratory symptoms 3) matched controls to the above two groups 4) operatives with chronic bronchitis. Byssinotic operatives demonstrated a decrease in FEV(1) across both shifts, with an increase in BR across the first shift of the week and a decrease in BR across the fourth shift. Control operatives showed little variation in spirometry but those who did react to histamine showed a increase in BR across both shifts.