Guinea pigs exposed acutely to an aerosol of cotton dust extract (ACDE) show a bronchoconstrictor response. The present work examines the response of guinea pigs to this same dose of ACDE divided into six equal 1 min inhalations spread over 6h. Specific Daily changes in sGaw was measured at several times each day. Daily changes in sGaw (bronchoconstriction) were observed, the largest being on the first and second days of each week. Changes in sGaw were also soon in a control group inhaling saline but they were much smaller. In addition, an airways hyper-reactivity to carbachol was seen in dust-treatment but not saline treated guinea pigs.