Benthic foraminifera (147 taxa) were investigated from the Caribbean Sea (Deep Sea Drilling Project; DSDP Hole 502A, depth 3051 m) and eastern equatorial Pacific Ocean (DSDP Hole 503B, 3672 m) over an interval between the terminal Miocene and the basal Pleistocene (5.5-1.7 Ma). To determine the influence over time of the Central American Isthmus (closure of the Isthmus of Panama occurring some time between 3.5 and 3.0 Ma) on the benthic fauna, the composition and diversity of the fauna as well as many physico-chemical variables were considered.