Time course of coated platelet formation. Unstimulated platelets or platelets stimulated with thrombin or thrombin plus convulxin for 1 or 3 minutes were analyzed by flow cytometry with (A) FITC-antifibrinogen or (B) PE-JON/A as described in “Materials and methods.” The absence of agonist is indicated by the dashed line, 1 minute by the thin line, and 3 minutes by the bold line. Regions M1 and M2 correspond to populations of activated and coated platelets, respectively.