OH megamasers with isotropic luminosities of up to 10^4 Lo are
 observed along the lines-of-sight toward the central regions of
 ultraluminous IRAS galaxies. These most luminous masers known to
 exist in the universe may be related to the molecular tori which
 are believed to surround active galactic nuclei. We intend to
 complement existing cm-wave data by observing the rotational OH
 tansitions toward selected `gigamasers', `megamasers', `kilomasers',
 and 18 cm OH absorbers. These observations will allow to investigate
 the OH megamaser phenomenon from an entirely new perspective. Whether
 we observe OH absorption or emission will greatly influence our
 knowledge on the ISM in distant ultraluminous starburst galaxies.
 A comparison of relative abundances can tell us in how far
 the typical line-of-sight differs from those amplifying the
 18 cm nuclear continuum emission and will allow to correlate
 the commonly used OH classification with its infrared excitation
 properties.