Recently discovered hydrothermal vents at 21 ¿N on the East Pacific Rise are discharging turbid waters at up to 400 ¿C; mixtures of the plumes with ambient seawater contain significant amounts of dissolved H2 and CH4, as well as He. The first grab samples of these waters were diluted 50--100 fold, but they contained as much as 20¿10-5 cc(STP) of H2 and 2¿10-5 cc(STP) of CH4 per gram of water. H2/CH4 ratios in the vents increase with temperature, a result that is tentatively attributed to chemical equilibrium and/or the redox state of the individual waters. The phase diagram for the NaCl-H2O ''surrogate-seawater'' system shows that liquid-vapor separation may take place prior to discharge, and mixing of a vapor phase with entrained cooler seawater would profoundly alter original concentrations of volatiles as well as dissolved salts. H2 and CH4 ratios to basalt-derived helium are respectively about 550 and 70 in these waters. The total fluxes from the world-ocean ridge system, estimated from the He-3 flux, are of the order of 1.3¿109 m3/y for H2 and 1.6¿108 m3/y for CH4. The CH4 flux so calculated is sufficient to replace the deep-sea methane in ~30 years, implying a very rapid bacterial consumption rate below the thermocline.