Measurements of pulmonary function were done in guinea pigs exposed to cotton dust. The method used permitted us to obtain characteristic breathing patterns which we classified as "obstruction", "restriction" or a mixture of both. Following a 6 hour exposure to cotton dust at 27 mg/m³, the pattern observed was restriction with obvious interruption of airflow. In 17 animals exposed at 21 mg/m³ of cotton dust 6 hours/day, 5 days/ week, we observed the following after 51 weeks of exposure: 4 animals were classified as presenting the obstruction pattern, 3 animals were classified as presenting the restriction pattern and 10 animals were classified as presenting a mixture of both patterns. Thus, both the acute and chronic effect of cotton dust were observed.