  We present a new technique for determining an upper limit for the mass of the
black hole in active galactic nuclei showing warm absorption features. The
method relies on the balance of radiative and gravitational forces acting on
outflowing warm absorber clouds. It has been applied to 6 objects: five Seyfert
1 galaxies: IC 4329a, MCG-6-30-15, NGC 3516, NGC 4051 and NGC 5548; and one
radio-quiet quasar: MR 2251-178. We discuss our result in comparison with other
methods. The procedure could also be applied to any other radiatively driven
optically thin outflow in which the spectral band covering the major absorption
is directly observed.
