ABSTRACT: The diet composition of 2 Antarctic octocorals Primnoisis antarctica and Primnoella sp. from the shelf of the eastern Weddell Sea (Antarctica) has been studied for the first time. Although mesozooplankton is very scarce inthe diet of these organisms, it seems to be important because of its high carbon content. Feeding experiments showed that components of the seston, including the finer fraction of suspended organic matter (ciliates, dinoflagellates and phytoplankton), arean important part of the octocoral diet. In P. antarctica, the diatom Fragillariopsis spp. accounted for 77% of the total number of cells captured, followed by dinoflagellates (20%), Nitzschia spp. (2%) and ciliates (1%). InPrimnoella sp., dinoflagellates were consumed preferentially (92%), followed by ciliates (6%) and centric diatoms (2%). Biomass consumed, however, was low (1.11 x 10^-5 mgC polyp^-1d^-1 for P. antarctica and 1.34 x 10^-4 mgC polyp^-1 d^-1 for Primnoella sp.). In P. antarctica, the small plankton food covers approximately 49% of the daily energydemand. The ability of these suspension feeders to take small cells at lower concentrations may allow them to remain seasonally active for considerably longer periods than previously thought.