[11C]Choline is a potential tracer to detect tumors, especially brain and prostate cancers. The metabolism of [11C]choline defines the accumulation pattern of [11C]choline in tumors depicted by positron emission tomography. Choline is a precursor of phosphatidylcholine that is a major constituent of membrane lipids. Membrane lipid synthesis as well as DNA synthesis is activated during cell proliferation. We investigated the relation between [14C]choline metabolism and proliferative activity using 10 tumor cell lines and fibroblasts. [14C]Choline uptake was higher in tumor cells than in fibroblasts and was correlated with the proliferative activity, though the sensitivity of [14C]choline uptake to proliferative activity was less than that of [1-14C]acetate. [14C]Phosphocholine produced from [14C]choline by phosphorylation mainly contributed to this accumulation. [11C]Choline can be used for the evaluation of tumor proliferation through estimating choline kinase activity.