The induction of organ system toxicity by the subchronic inhalation of diethylamine (109897) (DEA) vapors was studied in rats. Fischer- 344-rats of both sexes underwent inhalation exposure to DEA vapors at concentrations of 0, 25, or 250 parts per million (ppm) 6.5 hours per day, 5 days per week, for a period of 24 weeks. Male and female animals randomly selected from each exposure group were sacrificed after 30, 60, or 120 days of treatment. During the first 2 weeks of testing, rats exposed to DEA at a concentration of 250ppm did not gain weight; however, the rate of weight gain among these animals was greater than among controls thereafter, although the mean body weights of both sexes remained depressed throughout the experimental period. Sneezing, lacrimation, and reddening of the nose were also observed among animals undergoing exposure to DEA at the 250ppm concentration, with histopathological examinations revealing lesions of the nasal mucosa, primarily consisting of squamous metaplasia, suppurative rhinitis, and lymphoid hyperplasia. Blood urea nitrogen was elevated among both male and female rats undergoing exposure to DEA at a concentration of 250ppm for a period of 24 weeks. The authors conclude that DEA, inhaled at concentrations as high as 250ppm, does not induce cardiotoxicity in rats. It is recommended that further research be conducted for the purpose of investigating the time course, threshold, and incidence of nasal lesions among animals exposed to DEA.