Changes in the levels of biogenic amines in different brain regions and the cerebrospinal fluid in rats were measured after acute or chronic treatment with tricyclic antidepressants. After single or 3 weeks' treatment with imipramine or desipramine, blocks of tissues were obtained from seven regions of the brain (frontal cortex, corpus striatum, hippocampus, thalamus, hypothalamus, substantia nigra and cerebellum) immediately after collection of the cerebrospinal fluid (CSF) from the cisterna magna. The concentrations of biogenic amines and their metabolites (norepinephrine, epinephrine, dopamine, 5-hydroxytryptamine (5-HT), dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), 5-hydroxyindoleacetic acid (5-HIAA)) in brain tissues and the CSF were measured using the high performance liquid chromatography-electrochemical detection system (HPLC-ECD). Treatment with desipramine or imipramine caused major alterations in the concentrations of central norepinephrine or 5-HT and its metabolite, respectively. Brain regional responses were variable according to the kind of tricyclic antidepressants and the duration of treatment. It is noteworthy that chronic treatment with both desipramine and imipramine caused altered hippocampal concentrations of norepinephrine and/or 5-HT and its metabolites. Striatal DOPAC concentrations were also changed after acute or chronic treatment with both drugs. These results suggest that tricyclic antidepressants altered neurotransmission according to the brain region, and the hippocampal norepinephrine and 5-HT and/or the striatal dopamine may have a significant role for the expression of antidepressant action of tricyclic antidepressants.