To better understand how neuromodulators influence information processing we need to be able to monitor both chemical and electrical activity with high spatial and temporal resolution. This holds particularly true for the nucleus accumbens, a critical structure for motivated decision making. Subregions of the nucleus accumbens (including core and shell) have functionally distinct dopamine release characteristics, and sampling from these subregions with multiple electrodes has been difficult due to the size of existing glass or silica- insulated carbon fiber electrodes. To overcome this issue we have developed a high-density carbon fiber electrode array that can alternately monitor electrophysiological and dopaminergic activity in multiple subregions simultaneously. Specifically, we have developed a 16-channel array using a thin (t=50µm) flexible printed circuit board as the underlying substrate. At the end of this extension 16 carbon fibers, at a pitch of 132 um, are secured using silver epoxy. The fibers extend past the edge by 500µm, which is short enough for self-insertion, and are insulated with parylene-c. The tips of the fibers are then laser etched to re-expose a carbon surface and treated with oxygen plasma to remove any remaining debris. The laser and oxygen plasma steps result in a low electrode impedance and eliminate the need to electrodeposit poly(3,4-ethylenedioxythiophene). This array has been implanted in n=3 animals to date. Implanted arrays have exhibited single unit activity, as well as signatures of dopamine activity using cyclic voltammetry while the animal is awake and behaving. Phasic surges in dopamine concentration (i.e. dopamine ‘transients’; indicative of dopamine release from burst firing of dopamine neurons) were also detected using fast scan cyclic voltammetry after the administration of a cocaine and raclopride mixture through a venous port. In n=1 rat, the brain was sliced with the electronics in place after chronic experiments to visual the position of electrode tips, and the neurons immediately surrounding them. Thus, the array allows for sampling of electrical and chemical activity from neighboring, but still distinct, neuronal populations. Increasing the electrode density and count will provide yet further information about the influence of dopamine over microcircuit computations.