Patients with HIV commonly have coagulation deficiencies. Most of the deficiencies are related to reduced amounts of protein S or to thrombocytopenia. We have identified therapies that may improve coagulation by increasing protein S and C levels. We have developed an assay to identify glycocalicin in plasma that can differentiate between thrombocytopenia caused by increased destruction of platelets and by decreased production of platelets. This assay allows the clinician to identify the potential cause of the platelet defect and to treat the platelet abnormality by specific therapies; e.g., platelet transfusion, intravenous gamma globulin, and the use of vincristine and recombinant thrombopoietin. To date we have assayed blood from 50 HIV-positive adults and 49 HIV- positive children. We have found that some individuals have high glycocalicin and low platelet counts, while others have high glycocalicin and normal platelet counts. This test may be able to detect thrombocytopenia before the platelet count is clinically low.