Radiolaria were examined throughout the Plio-Pleistocene of Deep Sea Drilling Project (DSDP) Site 609. Eight radiolarian datum-levels (first and last appearances) were identified, some for the first time in the North Atlantic. The recognition of these datums allows correlation between the Atlantic, Pacific and Indian oceans, through a previously published zonal scheme (Johnson et al. 1989). Zones NR1 to NR11 were recognized, although some zones had to be combined (NR1–2 and NR8–10) due to the absence of some stratigraphically important taxa. The relative abundance distribution of the radiolarian palaeoceanographical proxy Didymocyrtis tetrathalamus indicated three cool phases (0/0.56–0.75 Ma, 1.2–1.33/1.69–1.86 Ma, and 2.14–2.32/3.73– > 4.1 Ma) interrupted by two relatively warm episodes (0.56–0.75/1.2–1.33 Ma and 1.69–1.86/2.14–2.35 Ma). These fluctuations in sea-surface temperature (SST) correspond with palaeoclimatic events indicated by other proxies (e.g. Foraminifera), such as the onset of Northern Hemisphere glaciation. This study illustrates the usefulness of radiolaria in North Atlantic stratigraphical and palaeoceanographical analysis.