A 68-year-old woman with fulminant hepatic failure of unknown etiology was treated with a bioartificial liver assist device. Prior to treatment, she had a number of clinical and laboratory features that suggested a hopeless outcome. Treatment was associated with a dramatic change in her mental status, and her clinical picture improved progressively during 6 days of continuous therapy. Evidence of recovery of native liver function allowed the discontinuation of treatment, and she continued to improve for a further 3 1/2 days before her demise from septic shock. We propose that a metabolically active liver assist device is a logical and practical method for treating the critical phase of fulminant hepatic failure.