A Phase I clinical safety evaluation of the Excorp Medical, Inc, Bioartificial Liver Support System (BLSS) is in progress. Inclusion criteria are patients with acute liver failure of any etiology, presenting with encephalopathy deteriorating beyond Parson's Grade 2. The BLSS consists of a blood pump, heat exchanger to control blood temperature, oxygenator to control oxygenation and pH, bioreactor, and associated pressure and flow alarm systems. Patient liver support is provided by 70-100 g of porcine liver cells housed in the hollow fiber bioreactor. A single support period evaluation consists of 12 hour extracorporeal perfusion with the BLSS sandwiched between 12 hours of pre (baseline) and 12 hours of post support monitoring. Blood chemistries and hematologies are obtained every 6 hours during monitoring periods and every 4 hours during perfusion. Physiologic parameters are monitored continuously. The patient may receive a second treatment at the discretion of the clinical physician. Preliminary evaluation of safety considerations after enrollment of the first four patients (F, 41, acetaminophen induced, two support periods; M, 50, Wilson's disease, one support period; F, 53, acute alcoholic hepatitis, two support periods; F, 24, chemotherapy induced, one support period) is presented. All patients tolerated the extracorporeal perfusion well. All patients presented with hypoglycemia at the start of perfusion, treatable by IV dextrose. Transient hypotension at the start of perfusion responded to an IV fluid bolus. Only the second patient required heparin anticoagulation. No serious or unexpected adverse events were noted. Moderate biochemical response to support was noted in all patients. Completion of the Phase I safety evaluation is required to fully characterize the safety of the BLSS.