  We discuss the possibility of quantum transitions from the string
perturbative vacuum to cosmological configurations characterized by isotropic
contraction and decreasing dilaton. When the dilaton potential preserves the
sign of the Hubble factor throughout the evolution, such transitions can be
represented as an anti-tunnelling of the Wheeler--De Witt wave function in
minisuperspace or, in a third-quantization language, as the production of pairs
of universes out of the vacuum.
