Antibody bivalency is not required for selective binding to a subset of FVIII disulfide-bonded states. The monovalent Fab Fc versions of antibodies, BO2C11 and KM33, were coupled to magnetic beads, incubated with recombinant FVIII and the bound and unbound FVIII fractions collected. Incidence of unformed disulfide bonds in the bound vs unbound FVIII (n = 1 experiment). The mean values for the starting (total) FVIII are shown as crosses.