F344 rats are susceptible and ACI rats are resistant to PhIP(2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine)-induced ACF formation (Nagao, 1998). Targeting on susceptible gene for colon tumor on rat chromosome 16 (Nakagama, 1999), this congenic strain was established by backcrossing F344/Jcl, as a donor strain, and ACI/NJcl, as a recipient strain.