Mytilus edulis, Cerastoderma edule and Aequipecten opercularis were found to ingest zooplankton when suspended in mesh cages in the water column in the Firth of Clyde. Zooplankters were also found in the stomachs of bivalves that had been taken directly from their natural habitat. The bivalves consumed a wide range of zooplankton species, but selectively consumed smaller categories of zooplankton present. Condition of zooplankton in the stomachs of the bivalves varied with zooplankton species. A degree of larviphagy was evident, particularly in Mytilus edulis.