Twenty-one aromatic amines or derivatives were tested for long-term toxicity by dietary administration to male Charles River rats and male and female HaM/lCR mice. 2,4-Toluenediamine, o-phenylenediamine, o-toluidine, 2,4,6-trimethylaniline, 2,4,5-trimethylaniline, 2,5-xylidine, and 1-chloro-2-nitrobenzene led to tumors in one or more tissues in all three of these animal models. p-Toluidine, 4-chloro-o-toluidine and 1-chloro-4-nitrobenzene had varying degrees of activity, but in male and female mice only. 4-Chloro-4'-aminodiphenyl ether affected male rats and female mice, but there was no consistent dose response. 2,5-Dimethoxy-4'-aminostilbene led to many tumors in male rats but had only a questionable action in male mice. The effect of 3,3',4,4'tetra-aminobiphenyl in male rats was borderline; in the mice only males showed any response. In male mice 2,4,6-trichloroaniline had a fair degree of activity; tetrafluoro-m-phenylenediamine was somewhat less effective and m-toluidine had only questionable activity. 2,4-Xylidine increased lung tumors in female mice at the higher dose only. Four inactive compounds included m-phenyl-enediamine, 2,4-dinitrochlorobenzene, benzoguanamine, and dicyclopentadiene dioxide. 2,4,6-Trimethylaniline led to cirrhosis of the liver in rats only.