We investigated the effect of prothrombin complex concentrate (PCC, median 500 IU) and vitamin K (10-20 mg) or either on blood coagulation and clinical findings in 17 patients with major hemorrhagic complication during warfarin treatment. Their international normalized ratio (INR) at admission was median 2.7 (2.0-above 10.0). In 11 patients treated with PCC and vitamin K, INR decreased to median 1.13 (0.91-1.36) 10 min after the administration with elevation of plasma levels of coagulant factors II, VII, IX, X and protein C.INR decreased abruptly after the administration of PCC without vitamin K in two patients but it increased again 12-24 h after, with decrease of coagulant factors levels. In one of them, a hematoma of the brain enlarged with INR re-increase 12-24 h after the administration. In four patients treated with vitamin K alone, INR decreased slowly from 2.69 (1.03-3.35) to 1.28 (1.25-1.44) 12-24 h after the administration in parallel with gradual increase of the coagulant factors.PCC administration with or without vitamin K seems to be more effective in rapidly correcting increased INR levels than vitamin K treatment without PCC. PCC without vitamin K may result in re-increase of INR and clinical deterioration.