  We study the dynamics of 2D and 3D barred galaxy analytical models, focusing
on the distinction between regular and chaotic orbits with the help of the
Smaller ALigment Index (SALI), a very powerful tool for this kind of problems.
We present briefly the method and we calculate the fraction of chaotic and
regular orbits in several cases. In the 2D model, taking initial conditions on
a Poincar\'{e} $(y,p_y)$ surface of section, we determine the fraction of
regular and chaotic orbits. In the 3D model, choosing initial conditions on a
cartesian grid in a region of the $(x, z, p_y)$ space, which in coordinate
space covers the inner disc, we find how the fraction of regular orbits changes
as a function of the Jacobi constant. Finally, we outline that regions near the
$(x,y)$ plane are populated mainly by regular orbits. The same is true for
regions that lie either near to the galactic center, or at larger relatively
distances from it.
