  We present some phenomenological aspects of the pre-big-bang cosmological
model inspired by the duality properties of string theory. In particular,
assuming the spatial sections of the homogeneous background geometry to be
isotropic, we discuss the quantum production of perturbations of the background
fields (gravitons, dilatons, moduli fields), as well as the production of
particles which do not contribute to the background, which we call ``seeds''.
As such we consider the cases of electromagnetic and axionic seeds. We also
discuss their possible observational consequences, for example, we study
whether they can provide the origin of primordial galactic magnetic fields, and
whether they can generate the initial fluctuations leading to the formation of
large-scale structure and the measured cosmic microwave background
anisotropies. We finally analyze axion and photon production in four
dimensional anisotropic pre-big-bang cosmological models.
