Observations are made on the distribution and variability in the Globigerinoides-Orbulina group in the Middle Miocene (Badenian) of Central Paratethys. The analysis of distribution and morphological diversity of planktic foraminifera versus environmental conditions prevailing in the Badenian of the studied area suggests that regional differentiation of the microfauna was controlled by bathymetric (or bathymetry-related) conditions and the stratigraphic - by climatic and, on a smaller scale, bathymetry-related ones. The differentiation is found within systematic groups (genera and species) of the analysed microfauna. In the case of foraminifera most sensitive to the above changes (representatives
of Globtgertnotdes), it is also traceable in their final, adult morphology. The phenotypic nature is ascribed to the bioseries Globigerinoides-Praeorbulina and Orbulina or Velapertina, i.e. Globigerinoides-Orbulina group.

Key words: Planktic foraminifera, Miocene, Central Paratethys, biochronology, ecology, taxonomy.