  We present evidence in favour of a link between the luminosity radiatively
dissipated in the central engine of radio-loud Active Galactic Nuclei and the
kinetic power in their jets. This piece of evidence is based on the relation we
find between the luminosity in broad emission lines and the kinetic power in
pc-scale radio jets, for a sample of radio-loud quasars for which suitable data
are available in the literature. We find that the ionizing luminosity and the
kinetic one are of the same order of magnitude, suggesting that the processes
responsible for them are somehow related. A strong magnetic field in
equipartition with the radiation field could be responsible for regulating both
processes. BL Lac objects seem to follow a similar behaviour, but with
comparatively fainter broad line emission.
