A self-potential survey made in the Long Valley caldera produced an anomaly derived from a dipolar source superimposed on potentials negative in polarity in relation to the area outside the caldera. The dipolar anomaly, consisting of negative and positive components differing amplitude by approximately 1 V, is centered over a resurgent dome in the west central part of the caldera. The exact nature of the potential source is unknown; however, electrofiltration processes caused by movement of heated groundwater that gives rise to streaming potentials are thought to be the principal cause of the dipolar anomaly. Diffusion potentials resulting from concentration differences between rising volcanic water and descending meteoric water may be responsible for the negative potentials measured within the caldera. Potential increases as high as 1100 mV were observed across the perimeter of the caldera.