  In this paper we demonstrate the possibility of inferring the presence of
Keplerian gaseous disks using optical ground-based telescopes properly
equipped.
  We have modeled the peculiar bidimensional shape of the emission lines in a
sample of five S0-Sa galaxies as due to the motion of a gaseous disk rotating
in the combined potential of a central point-like mass and of an extended
stellar disk. The value of the central mass concentration estimated for four
galaxies of the sample (NGC 2179, NGC 4343, NGC 4435 and NGC 4459) is ~10^9
Msolar. For the remaining galaxy NGC 5064 an upper limit of 5*10^7 Msolar is
estimated.
