A low molecular weight heparin (Fragmin, Kabi-Vitrum) with a mean molecular weight of 4,000-5,000 D has been investigated in healthy volunteers and in patients with DVT. We found a T 1/2 of 4 hours and a high bioavailability after subcutaneous injection in volunteers. In a randomised study, patients with phlebographically verified DVT, 120 U(anti-FXa)/kg Fragmin injected twice daily was found to be as effective as 240 U/kg, 12 h standard heparin as continuous infusion in preventing DVT progress. No major bleedings were seen in the Fragmin group. We conclude that Fragmin administered subcutaneously twice daily results in adequate anticoagulation and is safe and practical in the treatment of DVT.