Aim: To study whether the levels of striate dopamine neurotransimitters changed rhythmically in mice so as to provide experimental data to understand the function of dopaminergic neurons in the substantia nigra. Methods: The experiment was finished in the Department of Neurobiology of Beijing Institute of Geriatrics, from April to August 2004. Sixty C57 BL/6J mice housed under controlled conditions (light-dark cycle: 12-12 hours). Two weeks later, mice were divided into six groups and sacrificed at six different times during the 24-hour period (9:00, 13:00, 15:00, 21;00, 1:00, 5:00). The striatum was removed by dissection. The dopamine, 3, 4-dihydrophenylactic acid and 5-serotonin levels in the striatum were extracted with perchloric and assessed by using high performance liquid chromatography with electrochemical detection. The protein content in the striatum was detected with Lowry method. The concentrations of dopamine, 3, 4-dihydrophenylactic acid and 5-serotonin were expressed by actual content/protein content (μg/g), and the experimental data were expressed by mean value ± standard deviation. Results: All 60 mice were involved in the results. 1 The level of DA in striatum changed in 24 hours. The lowest level of DA was showed at 1:00 [(125.59 ± 5.29) μg/g], there was significant difference as compared with those at 9:00 and 12:00 [(151.34 ± 3.35), (147.68 ± 2.5) μg/g, P < 0.05], and reached to the peak at 9:00. 2 The level of 3, 4-dihydrophenylactic acid changed in 24 hours. The lowest level of dopamine was showed at 1:00 [(6.59 ± 0.32) μg/g], and there was significant difference as compared with that at 9:00 [(9.71 ± 0.62) μg/g, P < 0.05]. 3 There was no significant difference in the level of 5-serotonin (P > 0.05). Conclusion: There are rhythmic variations in the dopamine and 3, 4-dihydrophenylactic acid levels striate in mice, but not in 5-serotonin. The result indicates that dopaminergic neurons have the character of circadian rhythm, which indicates a regulation of dopamine metabolism by biorhythm.