SummaryA simple method for quantitating pletelet adhesiveness to glass is described. The use of minimally manipulated native whole blood and direct counting of adherent platelets are principal features of the method. Normal values for platelet adhesiveness to glass both in the absence and presence of added ADP are given. Without ADP, abnormally low platelet adhesiveness values were observed in afibrinogenemia, thrombasthenia, uremia, homocystinuria and in some patients with von Willebrand’s disease or Hageman trait. Under the same test condition, abnormally elevated values were found in some patients with von Willebrand’s disease or diabetes mellitus. With added ADP, which induced aggregation of some platelets in the blood, abnormally low platelet adhesiveness values were observed in thrombasthenia and one diabetic patient, while abnormally high values were found in von Willebrand’s disease, and in one patient with homocystinuria. The test for platelet adhesiveness performed with added ADP may have diagnostic value for patients with von Willebrand’s disease.