The benthic oxygen demand and inorganic nutrient release have been investigated in the coastal zone of the Mid-Atlantic Bight of the United States using in situ and ship-board incubations t,o estimate fluxes across the sediment-water interface. Oxygen demand ranged from ca. 70 nil m-2 hr-1 nearshore in warm (25 "C) muddy sediments to ca. 4 ml m-? hr-1 in cold (6 "C), coarse-grained sediments offshore. Ammoniumionflux was out of the sediments in all but 4 of 29 incubations, while nitrate was often found to be utilized within or on t,he sediments, decreasing in 10 of 29 incubations. Those locations with fluxes of nitrate out of the sediment had concentrations in the pore water that were generally high, sometimes u p to several mM 1-*. Nitrate fluxes were always well below those of ammonia, even where high almost equivalent concentrations of both NH4 and NO:, were found a t the same locale.On George's Bank only 13 "/o of total N demand b y the phytoplankton was estimated to be supplied by the benthos, whereas in New York Bight the supply amounted to 42 "/o of the demand. This difference can be attributed t o higher pelagic biological and advective (mixing and upwelling) inputs to George's Bank compared to the relatively well stratified New York Bight in late summer and autumn.