A double blind cross over study with suloctidil (Sulocton, Continental Pharma) and placebo was carried out for 6 months in 31 patients with idiopathic recurrent vein thrombosis. They were previously unsuccessfully treated with vitamin K antagonists (VKA) (18 patients) or acetylsalicylic acid (ASA) (13 patients) combined or not the a fibrinolysis activator (theophylline nicotinate). Clinical features, ultrasonic venous flow and biological parameters were controlled monthly during the 6 month treatment. Relevant improvement of clinical, ultrasonic and biological parameters was only observed under suloctidil therapy: during placebo administration 12 patients developed new thrombotic events complicated in 2 by pulmonary embolism while none occurred under suloctidil therapy.