  We present results of an intensive spectroscopic variability campaign of the
very broad-line Seyfert 1 galaxy Mrk 926. Our aim is to investigate the
broad-line region (BLR) by studying the intensity and line profile variations
of this galaxy on short timescales. High signal-to-noise ratio(S/N) spectra
were taken with the 9.2m Hobby-Eberly Telescope (HET) in identical conditions
during two observing campaigns in 2004 and 2005. After the spectral reduction
and internal calibration we achieved a relative flux accuracy of better than
1%. The rms profiles of the very broad Balmer lines have shapes that differ
from their mean line profiles, consisting of two inner (v $\lesssim \pm{}$ 6000
km s$^{-1}$) and two outer (v $\gtrsim \pm{}$ 6000 km s$^{-1}$) line components
in addition to a central component (v $\lesssim \pm{}$ 600 km s$^{-1}$). These
outer and inner line segments varied with different amplitudes during our
campaign. The radius of the BLR is very small with an upper limit of 2
light-days for the H$\beta$ BLR size. We derived an upper limit to the central
black hole mass of $ M= 11.2 \times 10^{7} M_{\odot} $. The 2-D
cross-correlation functions CCF($\tau$,$v$) of H$\beta$ and H$\alpha$ are flat
within the error limits. The response of the Balmer line segments with respect
to continuum variations is different in the outer and inner wings of H$\alpha$
and H$\beta$. This double structure in the response curves - of two separate
inner and outer components - has also been seen in the rms line profiles. We
conclude that the outer and inner line segments originate in different regions
and/or under different physical conditions.
