Dicopper(ll) tetrakis(3,5-diisopropylsalicylate), (Cu(II)(2)(3,5-DIPS)(4), manganese(II) bis(3,5-diisopropylsalicylate), Mn(II)3,5-DIPS)(2) or combinations of them were used to treat gamma-irradIated mice in examining the possibility that combination treatments might be more effective in increasing survival than treatment with either complex alone. Doses of 0, 10, 20, or 40 mumol of each complex per kilogram of body mass were administered subcutaneously in a factorial design before 9 Gy gamna irradiation, an LD(90) dose of irradiation. Doses of 0, 10, 20, or 40 mumol Cu(II)(2)(3, 5-DIPS)(4) per kg of body mass produced 12, 28, 28, or 36 % survival, respectively, while doses of 0, 10, 20, or 40 mumol (II)(3), 5-DIPS)(2) per kg of body mass prduced 12, 36, 20, or 24 % survival, respectively. However, the combination of 20 mumol Cu(II)(2)(3, 5-DIPS)(4) and 10 mumol Mn(II)(3, 5-DIPS)(2) produced the greatest survival, 48 %, which was 300 % greater than vehicle-treated mice (P=0.01). It is concluded that specific combination treatments can be used to maximize survival of lethally irradiated mice.