Prostaglandins and thromboxanes are oxygenated products of arachidonic acid, probably representing a phylogenetically old membrane-related defence mechanism. Several types of thrombocytopathy have been found to be associated with defects in platelet thromboxane formation or action: defects in cyclooxygenase activity (type I) or thromboxane synthetase activities (type II), and disturbed thromboxane action, caused by defects in the platelet thromboxane receptors (type III). All of these disturbances share a common failure of a platelet release reaction after stimulation by ADP or adrenaline++, as well as an absent or largely suppressed aggregation after arachidonic acid. The platelet count, platelet morphology and the nucleotide content of their storage granules are unchanged. This is a major difference to other congenital thrombocytopathies, such as thrombasthenia Glanzmann and storage pool disease. There is evidence of an autosomal gene defect mediating this disturbance by analysing family members. The clinical picture of this defect varies largely and is quite heterogeneous, even in the same individual. General findings are a prolonged bleeding time and bleeding tendencies which, however, are only very rarely associated with life-threatening situations. These data indicate that platelet thromboxane formation is an important, though not essential factor for the platelet release reaction and primary haemostasis.