Drilling at Site 549, located on the Goban Spur in the northern Bay of Biscay (Irish continental margin), penetrated an apparently continuous section of upper Eocene–lower Oligocene nannofossil chalks. The Eocene-Oligocene boundary as identified by nannofossils does not coincide with that recognized using planktonic foraminifers. Regardless of which biostratigraphic criteria are used, no dramatic nannofloral or planktonic foraminiferal change occurred at the boundary. There was a gradual transition from warm-water to cool-water assemblages through the late Eocene, with more intense cooling indicated by low-diversity assemblages in lower Oligocene sediments. A bottom-water temperature drop occurred in the late Eocene through early Oligocene as indicated by an 18O enrichment in benthic foraminifers, although some of this enrichment may have been caused by increased ice volume. A major benthic foraminiferal faunal change, from a Nuttallides truempyi–dominated assemblage to one dominated by wide- and long-ranging taxa, occurred in the early late Eocene. No major benthic assemblage changes occurred at the Eocene-Oligocene boundary.