The test substance included ammonium perfluoroalkyl carboxylates (CAS No. 68259-11-0) which contains 93 to 97% ammonium perfluorooctanoate (CAS No. 3825-26-1), and smaller amounts of ammonium perfluoroheptanoate (CAS No. 6130-43-4) and ammonium perfluorohexanoate (CAS No. 21615-47-4). The test substance was investigated in a mechanistic bioassay investigating extra hepatic tumor induction by compounds which induce peroxisome proliferation. In this mechanistic bioassay, 300 ppm of the test substance was fed to rats as part of their diet for 2-years. In addition to an ad libitum control, a second control group was pair-fed to the 300 ppm test group to control for the effects of reduced body weight. Increased incidences of combined (single, multiple) hepatic adenomas, Leydig cell adenomas, and pancreatic acinar cell adenomas were seen in the 300 ppm test group when compared to either the ad libitum or pair-fed controls. The tumor incidences (liver, testis, pancreas) were outside the historical control incidence range for DuPont Haskell Laboratory. In addition, age- adjustment statistics also support the conclusion that the tumor incidence was elevated for the liver (both controls), pancreas (pair-fed control), and testis (pair-fed control).