Using recent calibrations of the absolute magnitudes and temperatures and modern model atmospheres, six parameters of early-type stars have been computed. These parameters are the absolute luminosity, the radius, the flux of Lyman continuum photons, the excitation parameter, the fraction of the total energy emitted in the Lyman continuum, and the ratio of the total luminosity of the stars to the expected Lyman-alpha luminosity. The calculations have been performed for spectral types from B3 to O4 and for zero-age main sequence (ZAMS) stars, dwarfs (V), giants (III), and supergiants (I). Some of the above listed parameters have been computed also for central stars of planetary nebulae. A critical comparison with previous calculations is made. A brief discussion about the interpretation of the radio and infrared observations of Hii regions and planetary nebulae is also presented.