A study was conducted on the exposure response relationship between flour dust exposure and occupational symptoms by comparisons between exposure groups and estimated various components of variability. The total variation, variations between exposure groups, between workers, within workers, and between years of flour dust exposure in bakeries, flour mills, and packing stations were described. Three bakeries and four flour mills and packing stations were selected, and exposure groups were formed. Total dust and flour airborne allergen exposures were measured at all sites. The variation in total dust exposure was measured at the same three bakeries, but at just two of the four flour mills. Randomly selected employees wore personal samplers for particle monitoring. Altogether, 346 dust samples from 13 groups were collected. The levels of total dust exposure were highest in the mixing and packing sites of the flour mills and in the packing, mixing, and dough brake areas of the bakeries. The geometric means of the exposure groups varied from 0.3 to 9mg/m3. Within groupings, the within worker variation was larger than the between worker variation. The differences in total dust exposure between workers within the exposure groups were smaller than the differences between workers of the whole population. The largest variation was seen with the between group component, followed by the between day and between worker component and within worker component. The difference in total dust exposure between years was small. The authors suggest that additional research is needed to develop formulae using the various components to estimate the effect of the risk estimates.