Components of the fibrinolytic enzyme system were measured in 22 adult patients with leukaemia, 21 with myelomatosis and 10 with myeloproliferative disorders. Alterations compatible with disseminated intravascular coagulation (DIC) were found in half the patients with acute leukaemia and in some patients with myelomato. The changes of DIC did not appear to correlate with haemorrhagic features. The patients with idiopathic thrombocythaemiahad low fibrinolytic activity.