The distribution of temperature, salinity, density, dissolved oxygen, phosphate, silicate, and nitrate to 2000 m depth, and phytoplankton to 150 m depth is described in the region of an anticyclonic mesoscale eddy located in the Tasman Sea. Vertical discontinuities in the hydrological properties showed that the eddy had entrained several surrounding water types at the surface and at depths of up to 500 m. In particular, Bass Strait water normally found among the slope waters along the New South Wales coast was entrained by the eddy and transported to positions 200 km from the coast. The temperature and salinity of the eddy appeared to have been increased below the core of the eddy at depths of 300-600 m. due to the entrainment of and mixing with Bass Strait water. The distribution of density, oxygen, nutrients and phytoplankton in the central portion of the eddy between 60 and 240 m depth showed differences between adjoining positions which were attributed to vertical water movements within the eddy core. These movements appeared to be responsible for increases of phytoplankton biomass within the eddy, of up to 10 times that of the surrounding ocean.