R-parity violation and Peccei-Quinn symmetry in GUTs

We address the question whether it is possible in GUTs to obtain R-parity violation with a large {\Delta L{/}\Delta B} hierarchy of strengths so that the proton is stable while phenomenologically interesting L-violation is present. We consider versions of SU(5) with a built-in Peccei-Quinn symmetry spontaneously broken at an intermediate scale. The P-Q symmetry and the field content guarantee a large suppression of the effective B-violating terms by a factor \Lambda^3_{PQ}/M_PM^ 2_X while the effective L-violating terms stay large.