Supporting cells and hair cells from the low-frequency region of the guinea-pig cochlea were studied in vivo using intracellular recording and horseradish peroxidase marking techniques. Response characteristics of the support cells to tone bursts at various sound levels, frequencies, and durations were compared to hair-cell responses and potentials recorded in the organ of Corti fluid spaces. Findings suggest that the fundamental component of the support-cell response accrues from hair-cell-generated currents. This component of the support-cell response probably results from the flow of receptor currents across support-cell membranes through nonspecialized membrane patches, or across nonspecialized membranes and through gap junctions that couple adjacent support cells. Findings suggest a lack of electrotonic coupling between hair cells and neighboring support cells.