Fischer F-344 adult rats were exposed to airborne vapor concentrations of 0, 10, 25 or 75 ppm of DEEA for 14 weeks (6 hrs/day x 5 day's wk). Groups of animals were sacrificed immediately following the 14 week exposure as well as after a 4 week post-exposure or recovery period. No exposure-related microscopic changes were observed in any of the rats exposed to 10 ppm whether sacrificed immediately after the 14 week exposure or after a 4 week recovery period. Dose-related histological changes were observed in nasal turbinates and nasal cavities in rats exposed 14 weeks to 25 ppm or to 75 ppm. Such findings consisted of an increased incidence and severity, viz., minimal to slight to moderate, of focal hyperplasia alone and focal hyperplasia with squamous metaplasia of respiratory epithelium and multifocal mixed inflammatory cell infiltration of nasal mucosa. In the 75 ppm group, some rats experienced hypertrophy of goblet cells on the nasal septum and a low incidence of focal necrosis and exudate in the lumen of the nasal cavity.