Targeting ATC to two molecules on the tumor cells’ surfaces enhances killing. Targets were ex vivo cells from two patients with glioblastoma (08–32 and 08–33); both ex vivo lines expressed both HER2/neu and EGFR. The targets were exposed overnight (E:T = 5:1) to unarmed ATC or ATC populations armed with single BiAb (ATC-HER2Bi, ATC-EGFRBi, ATC-CD20Bi), a mixture of equal numbers of singly-armed HER2Bi- and EGFRBi-ATC (ATC-HER2Bi+ATC-EGFRBi) and a population of ATC simultaneously armed with HER2Bi and EGFRBi (ATC-HER2Bi,EGFRBi). Mean residual viability was determined by MTT assay. For both 08-32 and 08-33 target cells, overall analysis by 1-way ANOVA, p < 0.0001. Unarmed or CD20Bi-armed vs. HER2Bi-, EGFRBi and both doubly armed ATC, p < 0.0001 (***). HER2Bi vs. either doubly-armed ATC, p < 0.05 (only for 8-33). EGFRBi vs. HER2Bi+EGFRBi, p < 0.01 (**). EGFRBi vs. HER2Bi,EGFRBi, p < 0.05 (*). Comparisons between individual effector cells performed using Bonferroni multiple comparison test.