Abstract To characterize [methyl- 11C]choline ([ 11C]choline) as an oncologic PET radiopharmaceutical, [ 11C]choline uptake in regenerating livers after partial hepatectomy as a model of typical proliferating tissue and after CCl 4 insult as that of proliferating tissue with inflammation, was studied in rats. [ 11C]Choline, [ 18F]2-fluoro-2-deoxy-D-glucose ([ 18F]FDG) and [2- 14C]thymidine ([ 14C]TdR) uptake was studied in regenerating rat liver after 70% partial hepatectomy or CCl 4-administration. [ 11C]Choline uptake in regenerating liver after partial hepatectomy was significantly increased with [ 14C]TdR uptake as a marker of DNA synthesis at 18 hours after surgery. On the other hand, the uptake was not accelerated by CCl 4-administration, though it significantly increased [ 14C]TdR uptake. There were no differences of [ 11C]choline uptake acceleration following partial hepatectomy among the three parts of the regenerating liver. [ 18F]FDG uptake was accerelated in the regenerating liver on either partial hepatectomy or CCl 4-administration. The magnitude of the increase in [ 18F]FDG uptake in the regenerating liver induced by partial hepatectomy was greater than that for [ 11C]choline. [ 11C]Choline uptake in the liver was accelerated by partial hepatectomy, but not by CCl 4-administration. This might be expected given that the differentiation between proliferating tissues such as tumor and inflammatory tissue was possible by [ 11C]choline-PET.