In a search for more active radioprotective compounds, we have prepared and examined a series of model molecules in which the radioprotective beta-aminothiol unit (free or derivatized as acetate or phosphorothioate) is tethered to the DNA-binding chromophores quinoline and acridine through links of variable length. The modifying activity of these 'hybrid' molecules was estimated by measuring the formation of 8-oxo-2'-deoxyguanosine (8-oxodGuo) in double-strand DNA upon exposure to gamma-rays in oxygen-free solution in the presence of the drugs. We show that all hybrid molecules protect the guanine moiety from oxidation more efficiently than the parent beta-aminothiol units. The degree of protection is the highest for the molecules in which the thiol is linked to the strong binding intercalator acridine through a long polyaminochain.