Diurnal vertical migration of zooplankton is mainly influenced by light levels in temperate areas. In polar regions, light is continuous during the summer months. This study investigated whether diurnal vertical migrations were performed by some of the dominant members of the zooplankton of McMurdo Sound during the summer. Sampling was carried out at the edge of the permanent ice in McMurdo Sound. ... Sampling began at 11:30 am with drops of a 1mm mesh, free fall net from the surface ot the depths of 190, 160, 130, 100, 70, 40 and 10m. Light intensity was taken at each depth and recorded along with the simultaneous surface light intensity. Temperatures at each depth were also recorded. The procedure was repeated every four hours until 10 data sets were collected. In addition, the last four sets included samples to depths of 300 and 450m.