Modulation phase and Faraday rotation observations at Boulder of the ATS 6 radio beacon transmisions have measured the total slant electron content (N&tgr;) to the satellite and the content up to an altitude of about 2000 km (NF). Monthly median hourly values of N&tgr;, the residual plasmaspheric content above 2000 km (NP), and a factor F related to the electron profile shape and the earth's magnetic field are reported for 1974 to April 1975. The slab thickness &tgr; was calculated by using Boulder ionograms and numerical mapping estimates of the geographic variations of F0F2. The diurnal and seasonal variations of N&tgr;, Np, F, and &tgr; are discussed in terms of analytical models for the electron density profile shape. Representative models for day and night profiles in the summer, equinoctial, and winter seasons are presented, and their reliability is discussed.