This article is part of a study on cortical microcircuitry in which flash evoked potentials (FEPs) were recorded from the anesthetized rat visual cortex. The FEPs were subjected to current source density analysis (CSD). One of the limitations of the CSD method is the need for recording sites outside the sampling volume, in order to obtain a full description of the CSD distribution. This problem is acute in the neocortex where a tissue/fluid boundary exists. A simple solution is provided based on the fact that the field potentials decay minimally under the conditions of these experiments. In the neocortex the most superficial recording site and the deepest recording site are used to provide the extra recording sites necessary to obtain a full description of the CSD distribution. This approach when tested by summing the current sinks and sources across all layers of cortex produces excellent results, with significant reduction of the residual sinks and sources.