Two non-native comb-jelly species, M. leidyi and Beroe ovata, were recorded in the Gulf of Trieste in 2005 in addition to species known to occur from past records. It is presently difficult to say with certainty whether these two species have established viable populations in the northern Adriatic, since no population studies of Ctenophora have been carried out in this area. Thermohaline conditions and high prey abundance may favor establishment of M. leidyi in the northern Adriatic Sea; however, the concomitant presence of two species of Beroidae, which prey on M. leidyi, may prevent its explosive growth as has been observed in other new localities. Beroe ovata may not establish because salinity in the area may be too high and because it may compete with two native Beroe species for prey