Twenty-four DSDP sites with radiolarian-bearing upper Paleocene and/or lower Eocene sediment have been re-examined. None of the investigated sediment sequences contains the Paleocene/Eocene Series boundary. There are frequent coring gaps and/or poor recovery, and the radiolarian fauna is usually sparse and poorly preserved. Nevertheless, we have established the stratigraphic sequence of 70 lowest and highest occurrences in a 10-my interval spanning the boundary from the Paleocene Bekoma campechensis Zone to the upper part of the lower Eocene Buryella clinata Zone, and have related them to the calcareous nannofossil zonation. Using current nannofossil and foraminifera criteria to approximate the Paleocene/Eocene Series boundary, we have determined that there are six reliable, easily recognizable, and potentially useful radiolarian lowest occurrences that approximate the Paleocene/Eocene Series boundary: Calo-cycloma castum, Theocotylissa auctor, Lamptonium fabaeforme fabaeforme, Podocyrtis (Podocyrtis) papalis, Giraffospyris lata, and Phormocyrtis turgida.