Objectives: Recently, [methyl-11C]-(β-Hydroxyethyl)trimethylammonium ([11C]choline) has been discovered to be a very effective tracer in imaging various human tumors using positron emission tomography. Because of the short half-life of C-11, it is very difficult to use in a routine imaging procedure and needs a frequent synthesis of ["C]choline. This can be supplemented by the substitution of [11Ccholine with [methyS-18]fluorocholine. Here, we would like to report cell uptake and biodistribution of [11Ccholine and [18F]fluorocholine as a basic study. Methods [11C]Choline was prepared by the treatment of [11C]CHzI with N,N-dimethylaminoethanol and [18F]fluorocholine was synthesized from reaction of CHzBr[18F]F with N,N-dimethylaminoethanol. The radiochemical purity was checked by high performance liquid chromatography (HPLC). The biodistribution of [11C]choline and [18F]fluorocholine was determined in balb/c mouse at 5 min, 20 min, 40 min and 80 min. The cell uptake wa measured using glioma (9L) and colon adenocarcinoma (SW620). Results: The radiochemical purity was more than 98% after purification. In the liver, uptake did not change over time the uptake was 20/ID/g for [C]choline and 13%ID/g for [18F]fluorocholine. In the kidney, radioactivity decreased over tirne the uptake was 15%1D/g for [11Ccholine and 20%ID/g for [18F]fluorocholine, 80 min post-injection. The cell uptake of [11Ccholine was 4.93% for glioma (9L) and 18.69F for colon adenocarcinoma (SW620). For [18F]fluorocholine, 1.77% for glioma (9L) and 2.77% for colon adenocarcinoma (SW620). Conclusion: [11CCholine and [18F]fluorocholine showed a different cell uptake tendency, depending on cancer cell line. (Korean J Nucl Med 200135:185-191)