Measurement of the concentration of neurotransmitters such as dopamine (DA) and noradrenaline (NA) in the extracellular space of animals provides important information about their synthesis, release and metabolism in response to behavioral or pharmacological manipulations. Intracerebral microdialysis in conjunction with a highly sensitive analysis method such as high-performance liquid chromatography with electrochemical detection (HPLC-ECD) and capillary electrophoresis with laser-induced fluorescence (CE-LIF) detection was used to study the in-vivo release of catecholamines (DA and NA) and monoamine metabolites (3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA) and 5-hydroxyindole-3-acetic acid (5-HIAA)) within distinct brain regions of freely moving rats. Therefore, we optimized these methods and established a setup that enables separation and quantification of low DA and NA standard concentrations (1-200 nM). By using the CE-LIF system we were able to quantify DA and NA in low volume (<10 L) aqueous standards. In a next step we used HPLC-ECD for quantifying DA and NA and their metabolites in microdialysis samples from the rat nucleus accumbens (NAc). We were able to reliably measure basal extracellular levels of DA, NA and selected metabolites in microdialysates from this area. Moreover, the release of DA and NA was considerably enhanced in response to local depolarization by high potassium perfusion. Interestingly, we also found a significant increase of DA release in the NAc in response to swim stress indicating physiological functionality of released DA within this area under ethological relevant conditions. Thus, the present thesis has revealed the potential of combining microdialysis with highly sensitive analysis methods such as HPLC-ECD and probably also CE-LIF to detect and quantify extracellular levels of catecholamines (DA and NA) in microdialysates.