Bacterial and fungal populations of bale and lap fiber samples and their relation to bacterial-particle content in air during carding were studied. Doseresponse relationships of acute human pulmonary function to airborne bacteria and fungi were also studied. Washing with water, with bleach, or with alkali and bleach were equally effective In reducing the bacterial content of fiber and of air. Area of growth and grade of cotton were variably related to bacterial content of fiber and of air. Total and gram-negative bacterial content, but not fungal content, of air were highly correlated with pulmonary function responses of subjects exposed to dust generated during carding. Bacterial content in air was associated with bacterial content of bale and lap fiber for washed and unwashed cotton.