Biodistributions of radioactivity in blood and tumors of athymic mice bearing Ramos xenografts who were injected with either 1F5 (scFv)₄SA fusion protein, B9E9 (scFv)₄SA fusion protein, 1F5 Ab-SA chemical conjugate, CC49 (scFv)₄SA fusion protein, or directly labeled conventional 111In-DOTA-1F5 Ab. Mice in pretargeted groups (A) were injected with 1.4 nM of each unlabeled construct, followed 20 hours later by 5.8 nM CA, and 4 hours after that by 1.2 nM 111In-DOTA-biotin. In the directly labeled group (B), mice were injected with 1.4 nM of conventional trace-labeled 111In-DOTA-1F5 Ab at time 0 hours. Groups of 5 mice were euthanized 24, 48, 96, and 144 hours after injection of radiobiotin or 111In-DOTA-1F5 Ab. The radioactivity in blood and tumors were quantified by gamma counting, corrected for decay, and expressed as the % ID/g of tissue. 1F5 (scFv)₄SA fusion protein (•, tumor; ○, blood), B9E9 (scFv)₄SA fusion protein (▪, tumor; □, blood), 1F5 Ab-SA chemical conjugate (▾, tumor; ▿, blood), CC49 (scFv)₄SA fusion protein (▴, tumor; ▵, blood), directly labeled conventional 111In-DOTA-1F5 Ab (♦, tumor; ⋄, blood).