Serial peak expiratory flow measurements (PEFRS) have been used in the past to assess the effects of various inhaled agents upon the lungs in the occupational setting. In this small study cotton spinning operatives were supplied with mini-Wright Peak Flow Meters and were asked to perform serial measurements as often as they could during the day for a period of four working weeks (working days and rest days). Four operatives with symptoms of byssinosis (BYSS), sixteen operatives with work-related respiratory symptoms (WRRS) and eleven asymptomatic operatives (classified by a modified MRC Respiratory Questionnaire) supplied adequate records for analysis. The data was analysed for various indices of PEFR variability with respect to the first working day of the week, subsequent working days and rest days.