The radio beacon experiments on ATS 6 are capable of measuring the electron content in the ionosphere by the Faraday rotation technique and the group delay technique (also known as the modulation phase technique). The former is weighted by the earth's magnetic field and hence is not sensitive to electrons in the plasmasphere, while the latter is equally sensitive to all electrons along the radio path. By combining these two techniques the behavior of the plasmasphere can be continuously monitored. The nature and the limitations of these two techniques are simulated in a model study which is used to interpret experimental data. In this connection it has been found that the relative plasmaspheric electron content abundance ratio is a useful quantity for the purpose of diagnosing plasmaspheric conditions. Experimentally, two periods have been picked to show the behavior of the plasmasphere: one period in August 1974, during which it was magnetically quiet, and one period in October 1974, during which three successive magnetic storms occurred. The implications of the quiet day measurements on plasmaspheric parameters are discussed. Evidence is given that supports a large diurnal variation in transition height from below 1000 km at night to approximately 2000 km in the daytime at a mid-latitude station. During storms in October the plasmasphere was observed to be depleted, a condition followed by slow replenishment. The data are consistent with the inward movement of plasmapause to magnetic L shell 3.5.