In vivo voltammetry has been widely employed to monitor the effects of drugs on dopamine metabolism. In the present study, we report on the use of a newly designed assembly for implantation of carbon fiber microelectrodes for voltammetric measurements in freely moving animals. The assembly consists of an electrode holder and a fixed support (implanted stereotaxically) which is cemented to the rat skull. The working carbon fiber electrode is cemented to the electrode holder, and can be lowered into the fixed support for implantation into the brain parenchyma. This implantation assembly has been used to study the effects of tail-pinch on dopamine metabolism (extracellular DOPAC levels) in the nucleus accumbens and ventral tegmental area of the awake rat. Using this implantation assembly and 3 carbon fiber electrodes, oxidation peaks for ascorbic acid (-100 mV) and DOPAC (+ 100 mV) were recorded in both brain structures. Mild tail pressure for 7 min led to an increase in extracellular DOPAC levels in the nucleus accumbens. A smaller increase was observed in the ventral tegmental area. The DOPAC signals remained elevated for some time after removal of the stressor. This implantation assembly represents a convenient system for implanting carbon fiber electrodes in the freely moving rat, which can be employed to investigate the effects of behavioral manipulation on dopaminergic neurons at the terminal as well as at the cell body level. This microdevice could also be usefully employed for other in vivo electrochemical studies.