The concentration of airborne dust less ‘fly’ was measured simultaneously in the workzone and in 114 people's personal breathing zone in the dusty workrooms of two cotton spinning and one weaving mill during morning shifts on consecutive Mondays, Wednesdays and Thursdays of the working week. Exposure levels estimated from workzone samples correlated poorly with those measured in the personal breathing zone (Spearman correlation coefficient=0.41, P<0.001). Nevertheless, workzone concentrations of airborne dust less ‘fly’ might still be a reasonable index of average personal exposure in workrooms where people do not normally handle cotton fibre or cloth.