The concentrations of airborne dust and bacteria were determined in 12 flax scutching mills and in two milk processing plants in Normandy, France. A total of 308 of 340 flax workers and 111 of 113 milk processors volunteered to answer a respiratory questionnaire. Personal exposure to airborne dust in the scutching mills varied from 22.2 mg/m3 to 144 mg/m3 and areal concentrations from 8.92 mg/m3 to 47.1 mg/m3. The concentration of Gram negative bacteria ranged from 3970 (colony forming units) cfu/m3 to 67,900 cfu/m3 and that of total bacteria from 12,900 cfu/m3 to more than 600,000 cfu/m3. In all, 20% of the flax scutchers were found, on the basis of the questionnaire, to suffer from persistent cough and 25% from chronic phlegm production. The corresponding figures among milk processors were 3.6% and 4.5%. Unexpectedly, only 12.5% of the scutchers appeared to suffer from byssinotic symptoms even though they were heavily exposed to airborne dust and bacteria. The low prevalence of byssinosis might be due to self selection of the workforce or a relatively low concentration of the causative agent despite high airborne contamination.