  We consider the inclusive production of longitudinally polarized baryons in
${\vec p}p$ collisions at RHIC-BNL, with one longitudinally polarized proton.
We study the spin transfer between the initial proton and the produced baryon
as a function of its rapidity and we elucidate its sensitivity to the quark
helicity distributions of the proton and to the polarized fragmentation
functions of the quark into the baryon. We make predictions using an SU(6)
quark spectator model and a perturbative QCD (pQCD) based model. We discuss
these different predictions, and what can be learned from them, in view of the
forthcoming experiments at RHIC-BNL.
