A study of the macrobenthos and its environment in the Pamlico River estuary, North Carolina, included measurements of salinity, temperature, and dissolved oxygen, as well as the particle size and organic matter concentrations of the sediments. Salinity ranged from 1 to 20 o/oo, and temperature from 5 to 31C. Anoxic conditions in the bottom water overlying the deeper portions of the estuary occurred in the late summer. A preliminary sampling program in July, 1968 showed that the macrobenthos had both low diversity and low density because of harsh environmental conditions of salinity and sediment composition. On the basis of trellis diagrams, the estuary was divided into three areas: (1) an oligohaline zone dominated by Rangia cuneata and Nereis succinea, (2) a mesohaline zone with a Macoma balthica-Heteromastus filiformis-Nereis succinea association, and (3) a polyhaline zone at the mouth of the estuary characterized by a Macoma phenax-Mulinia lateralis-Glycera dibranchiata association. A seasonal sampling program, using transects located in these communities, showed vast seasonal changes in species composition, range of distribution, density, and community delimitation caused by the new set of planktonic larvae in the estuary. (Author)