The article presents the results of a biostratigraphic study based on the distribution and joint occurrences of calpionellids, radiolarians and calcareous nannoplankton, in a time section around the Jurassic–Cretaceous boundary in the Hrusove section of the Cachticke Karpaty Mts. The results gained show that the boundaries of biozones established on the basis of studies of the above mentioned groups of micro- and nannoplankton are not synchronnous. The association of radiolarians (U.A.11) and calcareous nannoplankton (zone CC1 Nannoconus steinmanii occurs in the uppermost Tithonian, below the boundary of the calpionellid zones Crassicollaria/Calpionella, which in the conception of Remane et al. (1986) corresponds to the Tithonian–Berriasian boundary.