Direct current electrical experiments with electrode arrays deployed by a submersible (ALVIN) were used to determine the resistivity structure of the seafloor below, and vertical potential gradients in sea water above, the hydrothermally active TAG mound. Apparent resistivities of the sulfides at shallow depths (~10 m) below seafloor over the mound ranged between 0.18--0.21 ohm-m, compared to nearby basalt pillow apparent resistivities of 2.1--2.4 ohm-m. The potential differences between heights of about 18 to 27 m above the mound averaged +3.7 mV (voltage increasing with height), with variations between about -2.9 and +12.7 mV. ¿ American Geophysical Union 1996