We examine the characteristics of warping modes in the maser disc
at the centre of NGC 4258.
We find that the velocity field associated with the modes
is approximately vertical and that its amplitude decreases with radius.
This characteristic accounts for the observed position and velocity
distribution of the high-velocity maser features of NGC 4258.
We also find that the position-velocity diagram calculated for a disc
with a warping perturbation pattern is consistent with
the observed redward offset of the low-velocity maser features,
if the maser emission arises from the upper-half part of the disc.
keywords: Accretion, accretion disks --
Galaxies: individual: NGC 4258 -- Galaxies: nuclei --
Masers -- Waves
