Extracorporeal perfusion of pig liver lasting 4 hr, followed by isovolaemic exchange (6 litres in 1 hr) were employed in the management of coma in a case of acute virus hepatitis. Liver perfusion led to temporary regression of coma, whereas transfusion was followed by gradual improvement in the clinical picture; this was apparently not a direct consequence of the procedure adopted. Assessment of the degree of purification obtained with these two methods offers an explanation for the difference in their clinical effectiveness.