High-resolution spectra of 30 late-type and 9 early-type candidate members of the young (˜50-80 Myr) open clusters NGC 2451 A and B have been analyzed in order to complement our previous photometric and X-ray study. Cluster membership of these X-ray selected stars has been confirmed or rejected on the basis of radial velocity and Hα chromospheric emission. The metallicity of both clusters seems to be about solar - contrary to previous investigations. Lithium abundances have been determined by two different methods, namely curve-of-growth techniques and spectrum synthesis, yielding quite consistent results. The pattern of Li abundances versus effective temperature resembles that of the equally-old Alpha Per cluster, i.e., little Li depletion is seen for solar-type and earlier-type stars, while towards cooler stars Li is more and more depleted, possibly showing a star-to-star scatter below ˜ 5200 K. The hottest star in our sample shows a Li abundance ˜0.5 dex higher than the meteoritic value. Rotational velocities have been determined in order to investigate the supposed dependence of activity and Li depletion on rotation. Based on observations performed at the European Southern Observatory, La Silla/Chile.