The effect on abnormal coagulation tests of infusions of fresh-frozen plasma (F.F.P), prothrombin complex concentrates, and a combination of these treatments was compared in 30 patients with chronic liver disease undergoing needle biopsy. A single dose of F.F.P. (12 ml/kg body-weight) was found to be the least effective therapeutic regimen. The concentrate containing factors II, IX, and X was also not adequate, but the additional administration of factor-VII concentrate corrected the prothrombin-time (P.T.) and "Normotest" (N.T.) in most patients. However, this regimen did not correct the prolonged kaolin activated partial thromboplastin-time (K.P.T.T.). The results of tests for exploring both the extrinsic (P.T. and N.T.) and intrinsic (K.P.T.T.) coagulation systems only became normal after the combined administration of a lower dose of F.F.P. (8 ml/kg body-weight) and of both concentrates (12 units/ml). There was no clinical or laboratory evidence of thrombotic complications. No patient developed acute hepatitis or hepatitis-B surface antigen in the twelve months after biopsy. These results indicate that prothrombin-complex concentrates in combination with F.F.P. may therefore be used to allow liver biopsy to be performed safely in patients presenting with severe coagulation defects.