A diverse and well-preserved dinoflagellate cyst and acritarch record, comprising 35 genera and 104 species of dinoflagellate cyst and 14 acritarch taxa, is presented for the Lower Pliocene through Middle Pleistocene (4.00-0.53 Ma) of eastern North Atlantic Deep Sea Drilling Project Hole 610A. The Pliocene samples contain twice as many dinoflagellate cyst taxa than the Quaternary samples but far lower cyst concentrations. The disappearance of taxa during the latest Pliocene is likely to have been associated with global cooling. Eight biozones and four subzones are established, representing a level of detail that surpasses earlier studies. The zones are based mostly on highest occurrences, as these are most prevalent in the Pliocene and Lower Pleistocene. The subzones, based on both the acme and highest persistent occurrence of Habibacysta tectata, appear regionally useful within the Lower Pleistocene. The lowest occurrence of Impagidinium cantabrigiense is a potential marker for the uppermost Gelasian Stage (Lower Pleistocene). While this biozonation is intended primarily for use in the eastern North Atlantic, elements will be applicable across the higher-latitude North Atlantic where calcareous microfossil zonations have reduced reliability and resolution. Most of the stratigraphically useful taxa are illustrated, and selected species are described informally.