Optical and scanning electron microscopy have been used to show unexpectedly high quantities of fungal materials present on cottons field-grown in seven geographical locations of the United States. Differential staining with Cotton Blue (Aniline Blue) was used to optically show the presence of fungi. Scanning electron microscopy of particles on a filter from a Cotton particle analyzer (CPA) showed the presence of respirable fungal particles. Many of these particles were removed from the fibers in the mechanical cleaning process of the CPA and it is probable that similar cleaning procedures in cotton mills release large quantities of fungal particulates into mill air systems.