The antigen capture capacity of antibodies covalently immobilized on injection-molded polystyrene beads was evaluated. Bromoacetyl groups on the bead surfaces rendered them reactive to protein nucleophilic groups. The bromoacetyl surface exhibited up to a ten-fold greater capacity for protein compared to unmodified polystyrene, with no detectable dissociation such as occurs with simple adsorption. Biotinylated anti-fluorescein was immobilized on this surface both through direct covalent attachment and indirectly via streptavidin, which was first covalently attached to the bead. Comparisons of the resulting biological activity, normalized to the amount of anti-fluorescein on the bead, were made between the attachment methods and simple passive adsorption. The presence of the streptavidin spacer on the bromoacetyl surfaces improved the antigen capture capacity of antifluorescein, for fluoresyl-albumin by 45% compared to direct covalent linkage of the antibody to modified polystyrene and by 160% relative to antibody adsorbed on unmodified polystyrene.