Experiments were performed to determine whether exogenous cytidine (5')diphosphocholine (CDP-choline) could modify the release of dopamine (DA) in the striatum. Rats were divided into two groups, receiving either a standard diet (UAR 004) or the same diet supplemented with CDP-choline (250 mg/kg day) for 28 days. On the last day the dialysis probes were inserted in the striatum, and DA, homovanillic acid (HVA), and 3,4-dihydroxyphenylacetic acid (DOPAC) efflux were measured in the dialysis stream basally and during K+ depolarization (80 mM K+). Basal DA, HVA, and DOPAC did not show any difference between treated and untreated groups. Depolarization with K+ increased DA levels by up to 3,000% in the control group and by up to 4,770% in the CDP-choline-treated group (p < 0.05), and reduced extracellular HVA and DOPAC concentration by up to 45 and 35%, respectively, both in the untreated and CDP-choline-treated groups. These results show that long-term treatment with CDP-choline increases the K+ induced release DN and suggest, in accordance with previous research, that by providing exogenous choline and cytidine, CDP-choline modulates dopaminergic transmission.