The tissue composition of human liver has been analyzed by a highly resolving new technic, crossed immunoelectrophoresis, using potent anti-liver serum absorbed with human plasma. As many as 57 different constituents which were unrelated to plasma proteins were revealed. Liver extracts from cystic fibrosis patients showed significantly fewer components than did the normal tissue. Of the liver constituents detected by this method, six were identified as distinct enzymes, including 3 esterases, 1 glucosaminidase, 1 glucuronidase and 1 catalase. No consistent alterations in these liver enzymes were found in cystic fibrosis livers. Kidney, submaxillary gland and pancreas shared, respectively, 45, 16 and 18 antigens with liver, as determined by their cross-reactivity with the anti-liver serum. A single tissue esterase revealed in kidney with this antiserum was clearly distinct from the single predominant esterase seen in lung with this reagent.