INTRODUCTION Though both are parts of the Mediterranean basin, the eastern Mediterranean and the Black Sea form distinct units from both the hydrographic and the biological points of view. The Levantine basin — delimited by the Anatolian peninsula, the Syrio-Israelian shores and the Egyptian littoral — is the main basin of the eastern Mediterranean. We studied the Harpacticoida along the Israel coasts. Also we used the data of Brian (1927, 1928) from the Dodecanese, of Gurney (1927) from the Suez Canal zone, and of Steuer (1948) from Alexandria, in order to obtain a comprehensive survey of the levantine Harpacticoida. In the Black Sea we studied the Harpacticoida of the Rumanian shores and a few samples from the Bulgarian shores and from the pre-bosphoric zone. From our work and the data from the Russian shores (Czerniavski, 1868; Sovinski, 1904; Borutzki, 1960; Mordukhai-Boltovskoi, 1960, etc.), from the Bulgarian shores (Chichkov, 1921 ; Klie, 1937; Caspers, 1951 ; Valkanov, 1957) and other data from the Rumanian shores (Jakubisiak, 1938a, 1938b; Serban, 1959; Marcus, 1960, etc.) we are able to give a general survey of the fauna of the northwestern part of this sea — the most interesting from the biological point of view. Unfortunately, nothing is known about the Harpacticoida of the Anatolian coast of the Black Sea and almost nothing about the Caucasian shores. There are some data from the Sea of Marmara, thanks to the study of Noodt (1955b), but we have no data from the Aegean Sea. In the zoogeographical analysis and the ecological considerations we referred mainly to the thoroughly studied northern European seas and to