Field recordings from the dentate granule cell layer of in vitro brain slices of temporal lobe epileptic patients were evoked by antidromic stimulation. Tissue from the same specimen was stained by the Timm-sulfide method to assess the pattern and degree of mossy fiber reorganization into the supragranular layer. A wide range of physiological responses and Timm staining patterns was present across patients. A significant correlation was observed between the abnormality of antidromic responses, reflected by multiple secondary population spikes, and the degree of Timm staining of the supragranular layer. This relationship lends support to the hypothesis that mossy fiber synapses located in the supragranular layer may have functional implications for granule cell excitability in human epileptic tissue.