Abstract The relation between elastic amplitudes for polarized proton-proton collisions and spin-dependent scattering observables is studied near the forward direction with a view to providing information on particular amplitudes at low values of momentum transfer. Such information is particularly important, for example, in considerations relating to the use of the transverse single-spin asymmetry in estimating the beam polarization achieved by the increasing number of accelerators aspiring to oﬀer spin-polarized hadronic particles at higher energy. Elastic scattering, a process at the confluence of "soft" physics and QCD, and where the role of spin could be more significant and complex than previously thought, is becoming topical again at high energies, as it might give a link between the perturbative and nonperturbative regimes of QCD. This interest is further enhanced by the progress in the acceleration and storage of polarized proton beams at the new RHIC collider, and by the related problem of measuring the polarization of such beams. The spin-dependence of high energy $pp$ forward elastic scattering is associated to a number of critical features of small-angle differential cross sections, spin asymmetries and total cross-sections in definite initial spin states. Electromagnetic and hadronic forces are of similar magnitude at small scattering angles, and they interfere in the spin-averaged forward differential cross-section as well as in a number of spin-dependent asymmetries. Previous investigations on possible contributions of an hadronic spin-flip amplitude to the polarization asymmetry in the Coulomb-nuclear interference (CNI) region, are extended to include complete consideration of all helicity amplitudes near the forward direction, and comparison with experimental data is performed whenever possible.