Significant photochemical dissolution of particulate organic carbon (POC) from resuspended estuarine and deltaic bottom sediments recently has been reported (Mayer et al 2006, Kieber et al 2006). We report dissolved oxygen consumption measured during this "photodissolution" process. Irradiations of suspensions of bottom sediments from Atchafalaya Bay, LA, and the membrane fraction of phytoplankton cells, were conducted in a solar simulator. Dissolved oxygen, POC, and dissolved organic carbon (DOC) were measured at the beginning and end of each 24-hour irradiation. Dissolved oxygen levels did not change in dark controls but did decrease in irradiated suspensions in proportion to POC loss, with one mole of O_2 consumed for every 2-3 moles OC lost from the particulate phase. Suspensions of phytoplankton membranes and Mississippi river delta sediments were irradiated under air vs. nitrogen gas. POC photodissolution was inhibited in the anoxic algal membrane suspensions but was of similar extent in the oxic and anoxic sediment suspensions. The involvement of oxygen in this photodissolution reaction hence may be integral to photodissolution with some substrates and a side-reaction with others. The consumption of dissolved oxygen during photodissolution of particulates in the coastal zone may influence the formation of suboxic bottom waters in the northern Gulf of Mexico.