Polarized $\Lambda$-Baryon Production in pp Collisions

We study the production of longitudinally polarized Lambda-baryons in single-spin pp collisions at RHIC and HERA-N as a means of determining the spin-dependent Lambda fragmentation functions. It is shown that a measurement of the rapidity distribution of the Lambda's would provide an excellent way of clearly discriminating between various recently suggested sets of polarized Lambda fragmentation functions that are all compatible with present e^+e^- data. We also address the main theoretical uncertainties, which appear to be well under control.