  We present results from infrared spectroscopic projects that aim to test the
relation between the mass of a black hole, M_BH, and the velocity dispersion of
the stars in its host-galaxy bulge. We demonstrate that near-infrared,
high-resolution spectroscopy assisted by adaptive optics is key in populating
the high-luminosity end of the relation. We show that the velocity dispersions
of mid-infrared, high-ionization lines originating from gas in the narrow-line
region of the active galactic nucleus follow the same relation. This result
provides a way of inferring M_BH estimates for the cosmologically significant
population of obscured, type-2 AGN that can be applicable to data from
spectrographs on the next generation infrared telescopes.
