Inhibition of ¹²⁵I-VWF binding to fibrin by SpII and SpIII.¹²⁵I-VWF (250 ng/mL) and increasing concentrations of unlabeled SpII (•) and SpIII (▴) were incubated on filters without and with fibrin (37 μg) for 2 hours at 37°C. For each point nonspecific binding (< 3% of total binding) was subtracted from the total binding to obtain the specific binding. Results are expressed as percentages of specific binding of ¹²⁵I-VWF in the absence of competitor. Error bars indicate SEM.