The most interesting species in the flora of the Palace of Culture and Science in Warsaw. Fragmenta Floristica et Geobotanica Polonica 7: 117–128, Kraków. PL ISSN 1640–629X. ABSTRACT: In the present study the flora of the exterior horizontal surfaces (roofs, terraces, stairs) of the highest office building (231 m) in Warsaw was investigated. Some groups of species such as phanerophytes, higrophilous and most abundant species were distinguished. The above species differentiated relatively well the flora of the area studied (the Palace of Culture and Science) and other polyhemerobic habitats. A comparative analysis of the flora of the Palace and that of walls and roofs in other Central European cities was also conducted.