Effectiveness of standard heparin (SH) in patients (pts) with deep vein thrombosis (DVT) remains contreversial in regard with the subcutaneous (sc) or intravenous administration route.To determine the relation between initial (day 1 after the beginning of treatment) and achieved anticoagulation level with base-line to control (at day 10) phlebo-graphic score variations, we carried out a randomized study including 68 pts with acute (less than 2 weeks) DVT treated either by SH, 500 ui/kg/day or low molecular weight heparin (LMWH, CY 222, institut Choay, 750 u anti-Xa IC/kg/day), both given by 2 daily sc injections for 10 days. Plasma was collected at the middle (at 8 a.m) of 2 sc injections to evaluate aPTT (CK prest, STAGO) and anti-Xa activity (Stachrom, Stago). The results show that : 1/ Thrombus reduction was similar (thrombolysis more than 30%, 65% in SH pts and 64% in LMWH pts, p NS) ; 2/ in SH pts, phlebographic score variations were correlated neither with achieved anticoagulation level (mean aPTT of day 3, 5, 10) nor initial day 1 aPTT (R=-.33 and R = .03 respectively) ; 3/ in CY 222 pts, no modification of aPTT was observed during the 10-day treatment, and phlebographic score variations were correlated neither with initial nor achieved anti-Xa activity (R=.06 and R=.24 respectively) ; 4/ only 2 SH pts extended DVT and 1 patient in each group developed a recurrent pulmonary embolism in spite of a well initial or achieved anticoagulation level (aPTT >1.5 the control value in SH pts).In conclusion, SH- or LMWH-related anti coagulation (or antithrombotic) effect is certainly not the sole prognosis parameter for well achieving venous thrombolysis in patients with DVT.