External fibrinogen and HOCl-LDL induced aggregation. Washed platelets were prepared with (1.5 mg/mL, ▵) or without (□) added fibrinogen and then challenged with the combination of 1 μM ADP and 20 μg HOCl-LDL/mL. Aggregation was assessed either by light scattering (A) or by single-platelet disappearance (B; means ± SD from 3 platelet preparations).