We have investigated the relationship between LDL, Fibrinogen (Fg), and GpIIb/IIIa. GpIIb/IIIa was purified from human platelets by affinity chromatography. Binding was assayed by flow cytometry. Polystyrene micro beads (Bangs Lab.) were coated with GpIIb/IIIa. Fluorescein isothiocyanate (FITC) labelled LDL, fibrinogen and BSA (negative control) were used as a ligands. Percent bound Fg-FITC or LDL-FITC to GpIIb/IIIa coated micro beads were found to be concentration dependent, reaching saturationAt saturation concentrations inhibited binding of g-FITC to GpIIb/IIIa coated micro beads dose dependently (30% max. Ynhibition). Percent bound LDL-FITC to GpIIb/IIIa coated micro beads was also inhibited by Fg (50% max. inhibition). Percent bound Fg-FITC and LDL-FITC to isolated platelets gave similar results with GpIIb/IIIa coated micro beads. Addition of purified GpIIb/IIIa caused inhibition of LDL-FITC biding to isolated platelets. GpIIb/IIIa, Fg-rcceptor on platelet is also LDL-receptor.