Mycotoxicosis is a term used to define a toxic reaction due to the ingestion of toxins produced by fungi. Oral ingestion, however, may not be the sole means of exposure. We have recently observed ten patients who had inhaled massive amounts of fungi, which resulted in an apparent toxic pulmonary reaction. Immunologic studies showed no sensitivity to various fungal antigen preparations and histologic study of the lung showed a multi-focal acute process, with primary involvement of the terminal bronchioles containing large numbers of various spores. Cultures from lung biopsy material revealed at least five fungal organisms. A one to ten year followup indicates that avoidance of massive reexposure to fungal dust is the key to the prevention of recurrent pulmonary mycotoxicosis.