  Transverse single spin asymmetries in pp --> pion X processes, while on a
quite firm ground experimentally, are still a much debated phenomenological
issue. We consider them in a transverse momentum dependent factorization
scheme. After revisiting a previous result, we give new estimates of the
Collins contribution by adopting the latest information on the Collins and
transversity functions, as extracted from SIDIS and e+e- data.
