The contents of monamine transmitters in preoptic/anterior hypothalamic (PO/AH) area and in the serum of rats injected with thyroxine (T4, 1 mg/100 g body wt/d, for 10 d, hypodermic i.) and fed with methimazolum (10 mg/100 g body wt/d, for 15 d) were assayed by high pressure liquid chromatography with electrochemical detector (HPLC-ECD). It was found that the content of dopamine and homovanillic acid in PO/AH area showed significant increase (P less than 0.01) associated with a slight rise (P greater than 0.05) of 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA), and with no change of norepinephrine in the thyroxine group. After fed with methimazolum, the content of norepinephrine decreased significantly (P less than 0.05), but no obvious changes occurred in dopamine, homovanillic acid, 5-HT and 5-HIAA. By synchronous analysing of monamine transmitters in peripheral serum, it was showed that there was no significant linear relationship between the changes of monamine transmitters in the brain and in the serum. The correlation between thyroxine and methimazolum on the content of monamine transmitters and on the change of body temperature was also discussed.