During the February response cruise to Axial Volcano, methane and hydrogen concentrations within the plume were significantly elevated above background. CH4/3He ratios were found to be 5--10 times greater than previously reported values for unsedimented ridges. An average Δ13C value of -32.7¿0.8? was determined for CH4 concentrations > 10 nM and CH4/Mn ratios were determined to be 2.2. Hydrogen concentrations as high as 183 nM were measured; however most were < 10 nM. Microbial oxidation of methane was negligible (<0.001 day-1) during this sampling period. However, microbial hydrogen oxidation was sufficient to explain decreased H2 concentrations measured at 'older' downstream stations. ¿ 1999 American Geophysical Union