The tumorigenic activities of four representative heterocyclic amine food pyrolysates, 2-amino-6-methyldipyrido[1,2-a:3',2'-d]imidazole (Glu-P-1), 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), 2-amino-3,8-dimethylimidazo[4,5f]quinoxaline (MeIQx), and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), were assessed in the neonatal male B6C3F1 mouse and were compared with that of the potent human carcinogen, 4-amino-biphenyl (4-ABP). These aromatic amines were administered by i.p. injection at two dose levels on days 1, 8, and 15 after birth; and the incidence of tumors was examined at 8 and 12 months. Glu-P-1, IQ, PhIP, MeIQx, and 4-ABP each induced a significant incidence of hepatic adenomas, as compared to the solvent-treated (DMSO) control. Hepatocellular carcinomas were also observed with 4-ABP, SO, and MeIQx. Overall tumorigenicity was in the order: 4-ABP greater than Glu-P-1 greater than IQ approximately PhIP greater than MeIQx greater than DMSO. In the neonatal B6C3F1 mouse, these heterocyclic aromatic amines showed potent tumorigenicity after 8 and 12 months at total doses that were 5-10,000-fold less than those employed in standard chronic bioassays.