Acetate and hydrogen concentrations in the pore water of Leg 204 sites were elevated relative to non-gas hydrate–bearing sites where such measurements have previously been made. The maximum acetate concentrations occurred at Site 1251, an area to the east of SHR at just above the BSR, a zone of very high methane concentration. Acetate maxima or locally high concentrations of acetate occurred at the BSR at all sites, and frequently correspond with areas of gas hydrate accumulation and high methane concentrations. Hydrogen data are sparse and qualitative; however, they indicate that elevated concentrations of hydrogen exist in these sediments. It would be beneficial to allocate more samples for hydrogen analyses in future seafloor coring efforts.