Lithium abundances vs. T_eff. The medium trend of the Pleiades and the Hyades is represented according to Soderblom et al. (1993a) and Thorburn et al. (1993), respectively. The stars with a high level of the chromospheric activity () are marked as full circles, those with a weak level of activity () as open circles. Triangles denote the upper limits of the Li determinations. The stars, for which are not defined, are marked as small full circles.