  We observed a sample of three Brightest Cluster Galaxies (BCGs), Abell
1836-BCG, Abell 2052-BCG, and Abell 3565-BCG, with the Advanced Camera for
Surveys (ACS) and the Imaging Spectrograph (STIS) on board the Space Telescope.
For each target galaxy we obtained high-resolution spectroscopy of the Halpha
and [NII]lambda6583 emission lines at three slit positions, to measure the
central ionized-gas kinematics. ACS images in three different filters (F435W,
F625W, and FR656N) have been used to determine the optical depth of the dust,
stellar mass distribution near the nucleus, and intensity map. We present
supermassive black hole (SBH) mass estimates for two galaxies which show
regular rotation curves and strong central velocity gradients, and an upper
limit on the SBH mass of the third one. For the SBHs of Abell 1836-BCG and
Abell 3565-BCG, we derived M_bh=4.8(-0.7,+0.8)10**9 M_sun and
M_bh=1.3(-0.4,+0.3)10**9 M_sun at 1 sigma confidence level, respectively. For
the SBH of Abell 2052-BCG, we found M_bh < 7.3 10**9 M_sun.
