Zooplankton collections from 100 stations in Foxe Basin and immediately adjacent waters of the eastern Canadian arctic, made in 1955, 1956 and 1957, are considered. Available information on physical oceanography of the region is discussed, especially factors with apparent direct relationship to plankton distribution. Zooplankton standing crop on the two sides of Foxe Basin is estimated, and related to water movement, depth, ice cover and turbidity. Zooplankton quantity within the upper 50 m of the basin is estimated as about 50 mg/m3, the western section showing approximately twice the standing crop of the eastern area. Forty-eight species of zooplankton are recorded, dominated numerically by amphipods (12), copepods (10) and medusae (9). Copepods exceed all other groups in biomass, and are represented principally by the species Pseudalibrotus minutus, Calanus glacialis and Calanus hyperboreus. Other especially abundant and widely spread species are Aglantha digitale and Halitholus cirratus (medusae), Sagitta elegans (chaetognath) and Themisto libellula (amphipod). From the occurrence of plankton species and apparent water movements, it is concluded that Foxe Basin is a region of opposed arctic (polar water) and subarctic (mixed polar and Atlantic water) elements, the former entering the basin from the north and dominating most of the north and central parts of the region, the latter entering from the south and influencing chiefly the southernmost part of the basin but probably extending as a minor element up the east side to the northern limits of Foxe Basin. Differences in the zooplankton development in different years are related in part to variations in duration of ice cover