Catecholamines, such as dopamine, play an important role in the control and regulation of many nervous system functions. There is growing evidence that environmental pollutants significantly alter levels of this important neurotransmitter. High Performance Liquid Chromatography with Electrochemical Detection (HPLC-EC) is employed as a relatively simple and very sensitive method for the detection of dopamine in the brain tissue of organisms exposed to environmental pollutants. The procedure is designed to handle samples of brain tissue weighing only a few milligrams and requires minimal sample preparation. Compounds are separated on a 5 μm-C18column and detected with an amperometric detector containing a glassy carbon working electrode maintained at +0.6 V with respect to a Ag/AgCl reference electrode. The detector response occurs in direct proportion to the concentration of the sample compound. Performance of the HPLC-EC method is illustrated through the analysis of central ganglia from the marine mollusc, Aplysia californica, that have been exposed to polychlorinated biphenyls (PCBs). Aplysia were injected with an Aroclor mixture (Aroclors 1016, 1221, 1254 & 1260 1:1:1:1) at doses of 50, 100 or 200 mg/kg. The concentration of dopamine in ganglia were determined three days post injection. The highest dose of PCB exposure reduced dopamine concentrations to 49, 51 and 33% of controls in the pedal, cerebral and abdominal ganglia, respectively. In addition, a significant dose-dependent reduction in dopamine level was found in the pedal ganglia, the site of the largest concentration of dopaminergic neurons in Aplysia. The measurement of neurotransmitter levels with HPLC-EC provides a direct assessment of the potential neurotoxicological effects of environmental pollutants.