  We present a calculation of inclusive polarised and unpolarised cross
sections within pQCD and the factorisation scheme, taking into account the
parton intrinsic motion, k_T, in distribution and fragmentation functions, as
well as in the elementary dynamics. We show, in contradiction with earlier
claims, that the Collins mechanism is suppressed and unable to explain the
large asymmetries found in p(transv. polarized) p --> pion X at moderate to
large Feynman x_F. The Sivers effect is not suppressed.
