Microdosimetry can be an important tool in fundamental radiobiology towards an improved understanding of the primary mechanisms of radiation action. In addition, its applications in radiation protection and in clinical radiology have been of increasing importance. The variance-covariance method relates to such applications; it permits the determination of the dose averaged microdosimetric parameters in radiation fields of varying intensity. Measurements with the variance-covariance method are here reported for therapy electron beams with acceleration voltages from 5 to 20 MV. The experimental results are compared with Monte-Carlo simulations.