The present atlas comprises chromosome counts on plants from the Balkan Peninsula only. The Balkan Peninsula area covers Yugoslavia (Slovenia, Croatia, Dalmatia, Serbia, and Montenegro), Albania, Greece (Macedonia, Thessalia, Peloponesus, the Islands, including Crete), Bulgaria. European Turkey is excluded. The richness of the Balkan flora, (ca. 6500 species as estimated by Turrill (1929)) is due to several conditions such as: 1) an old flora with many species already dating from the Tertiary. 2) the changes in extent and level of the Mediterranean See. 3) the migration of elements from other flora's, like Pontic and European. 4) the inevitable influence of man. An extensive survey of these phenomena is given by Turrill (1929), and Polunin (1980). The Balkan flora nowadays consist of the following components: 1300 Western European species, 1000 Central European species, 2000 Mediterranean species, 2000 Balkan species, 200 Pontic species, 300 Oriental species, and about 20 North African species. Turrill pointed to the fact that there are ca. 1750 endemic species, a quarter of the flora. The endemic species especially attract attention. These elements may help to elucidate the history, and the development of the flora. Karyologically, only a small part of this flora has ever been studied. The table lists the species investigated and their origin. Those species are listed that correspond with those given by Flora Europaea vols. I?V. The table gives all chromosome counts up to and including 1980. The taxonomy and the nomenclature of the Flora Europaea is followed. Synonyms are added as far as necessary. The percentage of species investigated ranges from 3.6 % (Albania) to 29 %. (Bulgaria); for the whole area 23 % seems to be a reasonable estimate.