AIMS/ BACKGROUND OF STUDY The von Willebrand Factor (vWF) is a large procoagulant multimeric glycoprotein synthesized exclusively in endothelial cells and megakaryocytes and stored in the Weibel –Palade bodies and platelet -granules, respectively1 . It serves two major functions in haemostasis, as carrier for VIII and as the ligand mediating platelet GPIb adhesion to collagen.2 The mechanisms that control plasma vWF: Ag concentration are multifactorial and poorly elucidated. Approximately 70% of variability is due to genetic factors3 , of which the ABO blood group has been identified as the major influence.4 Several studies have consistently reported that group O subjects have lower plasma vWF levels than their non –group O counterparts.5 From those reports, it was also observed that the normal range of vWF: Ag in group O individuals extends below 50 IU/dl, which is commonly accepted as the lower limit of normal. Accordingly, O group individuals may or may not be at greater risk for bleeding and are more likely to be diagnosed with mild von Willebrand Disease. However, there is no demonstrable effect of Rh blood group on plasma vWF: Ag level in the literature. This study therefore aims to establish the ABO –specific, and possibly RhD– specific reference range for vWF: Ag in Blood Donors for the purpose of determining its clinical value in estimating the prevalence of von Willebrand Disease. Methodology: A cross-sectional analytical study was conducted to determine the vWF: Ag levels and some haemostatic parameters among Blood Donors at University of Uyo Teaching Hospital, Uyo – Akwa Ibom State. One hundred (100), subjects who met the inclusion criteria were recruited into the study. A pre-tested and structured questionnaire was administered to each participant. Complete blood count along with red cell indices were determined using Haematology auto-analyzer. Baseline Prothrombin Time (PT) and Activated Partial Thromboplastin Time (APTT) were done using PT/APTT reagent as described in Dacie and Lewis.69 Determination of ABO and RhD Blood Grouping was done using the standard tube method. 70 von-Willebrand Factor Antigen Levels were assayed using a quantitative sandwich immune assay technique. Data obtained were analyzed with EPI info version 3.5.1 August 2008 software. Chi-square was used to determine significant association and a P-value of <0.05 was considered statistically significant