Hydroxyurea treatment and platelet clearance in PV and ET patients. The presence of leukocytes with intracellular platelets was assessed by flow cytometry in the blood of 7 patients studied before and after hydroxyurea treatment, as described in the text. Symbols represent the percentage of neutrophils (A) and monocytes (B) with intracellular platelet antigens. Filled symbols indicate patients with previous thrombotic episodes.