Manifestations of the plasmapause in the topside ionosphere are discussed. Light ion and electron troughs observed in the topside ionosphere by Ogo 6 on a predawn and a dusk pass are compared to equatorial electron density profiles deduced from whistlers observed at the same local magnetic time and within 1.4 hours in UT on the predawn pass and 1.1 hours in UT on the dusk pass. The plasmasphere was distended in a period of low geomagnetic activity, and the whislter profiles did not extend through the plasmapause if a significant one existed. On the predawn pass, coincidence of the NH+ and NHe+ troughs at a plasmapause just beyond the E value where the whistler-deduced equatorial profile ceased at 350 el/cm3 could have occurred if reasonable suppositions are made. However, the 'main trough' in Ne lay at a significantly lower L value. On the dust pass the NH+ trough lay well beyond the limit of the whistler profile, which reached down to approximately 200 el/cm3, and NHe+ showed only a steady decline with no trough. The Ne trough was shallow and coincided with the NH+ trough.