ABSTRACT: Calcareous nannofossil biostratigraphic studies are presented from 11 sedimentary sections, nine located in the Mediterranean area and one each from the middle latitude North and South Atlantic, respectively. The distribution patterns of middle to late Eocene calcareous nannofossils are studied by means of quantitative and semiquantitative methods. Our main goal was to test the biostratigraphic reproducibility of bioevents used in two classical standard biozonations, and to introduce new biostratigraphically useful biohorizons, resulting in a series of new middle latitude biostratigraphic events. The new zonal scheme substantially improves the available biochronologic resolution, doubling the current partioning based on the classical standard zonations. This study extends the terminal Eocene and Oligocene calcareous nannofossil zonal scheme proposed for the Mediterranean area (Catanzariti et al. 1997), into the middle Eocene. New age estimates are provided, which highlight the need to revise the present middle-late Eocene calcareous nannofossil biochronology. Two new species are described: Cribrocentrum erbae sp. nov. and Cribrocentrum isabellae sp. nov.