Feeding by the coastal ctenophorc, Mnemiopsis leidyi , on microplankton was investigated. Larval ctenophores (tentaculate stage) grew best and had the highest survival rates when offered a mixture of ciliates and copepod nauplii. Larvae did not survive when offered phytoplankton alone. Clearing of planktonjc ciliates by post-larval ctenophores was a function of the ciliate species and the size of the predator. Removal of small ciliates (3 ) had higher biovolume-specific clearing rates (0.5–1.5 1 cm −3 day −1 ) than did larger ctenophores fed the same ciliate species. During in situ incubations, adult M. leidyi removed ciliates, rotifers and copepod nauplii from natural microplankton assemblages. The data indicate that non-crustacean microzooplanlctoo are an important component of the diet of larval and post-larval locate cteoophores, particularly when copepod standing stocks are low.