External proton and 6,7 Li beams, of energies around 24 and 48 MeV respectively, were produced and characterized dosimetrically at the Tandem accelerator TANDAR in Buenos Aires and used for radiobiology studies on tumor and normal cell cultures. The beam monitoring instrumentation of a dedicated beam line is discussed. Relative biological effectiveness (RBE) values (at 10% survival) have been measured as functions of projectile energy (0–21 MeV) for protons and 6,7 Li ions for different tumor (PDV, PDVC57) and reference cell lines (V79). The RBE values for these cell lines have been determined here for the first time but are similar to those reported in the literature for other cell lines.