Electron density profiles and isodensity contours derived from Jicamarca incoherent scatter radar observations in Peru for October 1–2, 1970, are compared in detail with results from the Phillips Laboratory global theoretical ionospheric model. This model solves the ion continuity equation for O+ concentration through production, loss, and transport of ionization. The primary factor controlling the peak plasma density at Jicamarca is the vertical E×B drift, which drives the ionization upward during the day and downward at night. When we use the measured drift in the model, we achieve excellent results with the measured electron density profiles. We illustrate the sensitivity of the low-latitude plasma density calculations to changes in the vertical E×B drift and changes in the neutral winds. We also compare the calculated profiles and peak parameters with an empirical model, the International Reference Ionosphere (IRI). We illustrate several limitations associated with the IRI that contribute to its limited capability at the magnetic equator.