4 parameters of dust exposure in 2000 workers identified for the first time in years 1 to 3, of a 5 year longitudinal study of respiratory disease in Lancashire cotton spinning mills. The dust parameters identified were current work area and personal dust exposure and estimated cumulative work area and personal dust exposure. Cumulative dust exposures were calculated from retrospective data supplied by each of the mills included in the study. Retrospective personal exposures were calculated using this data and results of comparative performance of the two techniques identified in an earlier report. Dose response relationships have been identified between each of these parameters and prevalence of byssinosis and other work related respiratory symptoms.