Zooplankton was sampled intensively with an RMT 1+8M system in the fjord of Cumberland East Bay, South Georgia during late winter 1983 and summer 1987. In summer, biomass was highest in the surface 20 m, reaching 142 g dw/1000 m3. Copepods dominated the zooplankton comprising 96–99% by numbers, of which 80–90% occurred in the top 100 m of the 265-m water column. The small clausocalanid Drepanopus forcipatus was particulary abundant. With increasing depth the proportion of non-copepod biomass, principally Mysidacea and Amphipoda increased significantly. Biomass throughout the water column in winter was generally 4–5 times lower than in summer although again copepods, and in particular D. forcipatus and members of the Metridinidae, still numerically dominated the plankton. Biomass levels were some 2–3 times greater than those found in Antarctic oceanic regions but were comparable with estimates from some boreal fjords. The mixture of neritic and oceanic species encountered, and the seasonal presence of some gelatinous zooplankton, particularly ctenophores, appears typical of the community structure of many fjord ecosystems.