The introduction of Mediterranean pelagic copepod species into the Black Sea was reviewed with special reference to Acartia tonsa. About 60 zooplankton species and 40 phytoplankton species which are not typical for the Black Sea were discovered to have been transported from the Mediterranean Sea. Most copepod species were found only in the Bosphorus area of the Black Sea. A few species were observed in other regions as far as Crimea and Caucasus, but they were seldom. Some species can now be included in the list of the constant inhabitants of the Black Sea as had happened with their predecessors. In the present study, five copepod species, Microcalamus pusillus, Aetideus armatus, Euchaeta marina, Metridia lucens, and Oncaea obscura, were also recorded for the first time. All these species were found in the Bosphorus region. New data about occurence, distribution and abundance of the copepod Acartia tonsa which was recently discovered in the Black Sea are also given. The present study confirms that this species has now been naturalized in the Black Sea.