New methods of detecting local extracellular electron transfer rates in electrochemically active biofilms (EABs) are needed to quantify the role of microscale gradients in extracellular electron transfer. We utilized electrode-respiring Geobacter sulfurreducens biofilms as a model EAB to demonstrate local current measurement by depth using microelectrodes with a graphite tip covered by biofilm. We grew G. sulfurreducens biofilms on an electrode (electrode-biofilm) and on the tip of a microelectrode (microelectrodebiofilm) and monitored current generation. The microelectrode-biofilm current was negatively affected by the current produced in the electrode-biofilm; this resulted in a change in current, Delta. We found a 30% decrease in current from the top of the electrode-biofilm to the bottom of the electrode-biofilm. We attribute the current loss at the microelectrode-biofilm to exposure to local microscale conditions that reduced the ability of themicroelectrode-biofilm to participate in extracellular electron transfer. It is possible that such microscale gradients as pH, redox and acetate caused a 30% current drop between top and bottom. The new technique developed in this research provides a measure of the local impact of extracellular electron transfer occurring within a thick biofilm. (C) The Author(s) 2014. Published by ECS. All rights reserved.