The occurrence of mafic layers in peridotites constitutes an important compositional heterogeneity in the mantle, and their role in mantle melting and basalt generation is currently debated. We present field, chemical and isotopic data on pyroxenites and host peridotites from the western peridotite massifs of the External Liguride ophiolitic Units (Northern Apennines, Italy). Pyroxenites (mostly spinel-websterites) occur as cm-thick bands (up to 12 cm) parallel to the tectonite mantle foliation, and ,together with the peridotites, they are partially recrystallized at plagioclase-facies conditions. Whole-rock and mineral compositions are extremely heterogeneous, covering almost the entire compositional range of worldwide lithospheric pyroxenites (Mg# = 74-88, Al2O3 = 10-17 wt%, CaO = 7-20 wt%). The pyroxenite chemistry reflects high-pressure magma segregation of tholeiitic melts dominated by clinopyroxene crystallization. A multi-step, sequential leaching procedure on clinopyroxene separates enables us to remove partial contamination and provides reliable Sr isotope data. The Sr and Nd compositions of clinopyroxenes from pyroxenites and peridotites fall in the typical range of normal MORB (87Sr/86Sr =0.7023-0.7029; 143Nd/144Nd =0.5134-0.5128). Internal Sm-Nd isochrons on plagioclase-clinopyroxene pairs from two pyroxenites yield ages of 183±14 Ma and 177±12 Ma for the low-P mantle exhumation. On a slightly larger spatial scale, chemical and isotopic profiles through the pyroxenite-peridotite boundaries indicate cm-scale modification of the wall-rock peridotite, presumably related to emplacement of the pyroxenites. This suggests that deep melt intrusion can locally modify the host peridotites and introduce small scale compositional heterogeneity in a MORB mantle.