  We investigate the magnetic properties of quasi-one-dimensional quantum
spin-S antiferromagnets. We use a combination of analytical and numerical
techniques to study the presence of plateaux in the magnetization curve. The
analytical technique consists in a path integral formulation in terms of
coherent states. This technique can be extended to the presence of doping and
has the advantage of a much better control for large spins than the usual
bosonization technique. We discuss the appearance of doping-dependent plateaux
in the magnetization curves for spin-S chains and ladders. The analytical
results are complemented by a density matrix renormalization group (DMRG) study
for a trimerized spin-1/2 and anisotropic spin-3/2 doped chains.
