Diethyltoluene diamine (68479-98-1) was evaluated in a two-year dietary oncogenicity study on Sprague-Dawley rats (50/sex/group) fed diets containing 0, 10, 35 and 70 ppm of the test material. A statistically significant increase of the incidence in hepatocellular carcinomas and hepatic proliferative lesions (eosinophilic and basophilic foci), as well as follicular cell adenomas and follicular cell hypertrophy of the thyroid were observed in the high dose males. High dose males also showed: an increase in multifocal acinar atrophy accompanied by interstitial fibrosis and fatty infiltration in the pancreas; bilateral cataracts and moderate to severe keratitis of the eyes; increased incidence of multifocal medullary hyperplasia in the adrenals. One follicular cell carcinoma was present in a low dose male. Follicular cell hyperplasia and follicular cysts were increased in the thyroids of the mid and high dose males. Focal medullary hyperplasia was also seen among control rats.