In a case of Ehlers-Danlos syndrome, a platelet defect is described. It is characterized by a defect of ADP and platelet factor 3 release, absence of secondary curve in ADP, adrenalin and distilled water-induced aggregation and a defective collagen aggregation. It is pointed out that this defect, which occurs in primary thrombopathy, also exists in connective tissue diseases such as Ehlers-Danlos syndrome, osteogenesis imperfecta, etc