  A statistical analysis of the space-time distribution of absorption-line
systems (ALSs) observed in QSO spectra within the cosmological redshift
interval $z$=0.0--3.7 is carried out on the base of our catalog of absorption
systems (Ryabinkov et al. 2003). We confirm our previous conclusion that the
$z$-distribution of absorbing matter contains non-uniform component displaying
a pattern of statistically significant alternating maxima (peaks) and minima
(dips). Using the wavelet transformation we determine the positions of the
maxima and minima and estimate their statistical significance. The positions of
the maxima and minima of the $z$-distributions obtained for different celestial
hemispheres turn out to be weakly sensitive to orientations of the hemispheres.
The data reveal a regularity (quasi-periodicity) of the sequence of the peaks
and dips with respect to some rescaling functions of $z$. The same periodicity
was found for the one-dimensional correlation function calculated for the
sample of the ALSs under investigation. We assume the existence of a regular
structure in the distribution of absorption matter, which is not only spatial
but also temporal in nature with characteristic time varying within the
interval 150--650 Myr for the cosmological model applied.
