The present prospective study was designed to evaluate the effectiveness and safety of prothrombin complex concentrate (PCC) for emergency reversal of oral anticoagulation with phenprocoumon, a long-acting coumarin. Patients were eligible for study entry if they required emergency reversal of phenprocoumon anticoagulation because they needed invasive surgical or diagnostic procedures or were actively bleeding. Patients received one or more infusions of pasteurized nanofiltered PCC (Beriplex P/N). Primary study endpoints were changes in International Normalized Ratio, Quick value, factors II, VII, IX and X, and protein C 10, 30 and 60 min following PCC infusion. Eight adult patients were enrolled, seven requiring urgent invasive procedures and one experiencing intracranial bleeding. In the first infusion, patients received a median 3600 IU PCC at median infusion rate 17.0 ml/min. Mean (SD) baseline International Normalized Ratio was 3.4 (1.2). The International Normalized Ratio 10 min after PCC infusion declined to 1.3 or less in seven of eight patients and to 1.4 in one patient. After PCC infusion, the Quick value increased by a mean of 57% [confidence interval (CI), 45-69%], circulating factor II concentration by 85% (CI, 68-103%), factor VII by 51% (CI, 40-62%), factor IX by 61% (CI, 47-76%), factor X by 115% (CI, 95-135%) and protein C by 100% (CI, 82-117%). Clinical effectiveness of PCC treatment was rated 'very good' in seven patients and 'satisfactory' in one. No thromboembolic or other adverse events occurred. PCC treatment rapidly, effectively and safely reversed phenprocoumon anticoagulation in patients undergoing urgent invasive procedures or actively bleeding.