The occurrence of antigen reacting with antibody to porcine neurophysin.

1. Antiserum was raised in rabbits to neurophysin prepared from posterior pituitaries of pigs. The presence of antibody reacting with porcine neurophysin was demonstrated in precipitation, gel diffusion and immunoelectrophoretic tests.2. The antibody was species specific and did not react with protein from rat, bovine or guinea-pig neurohypophyses.3. The occurrence of antigen reacting with anti-neurophysin serum was demonstrated in acetic acid extracts of porcine kidney but there was no evidence for the presence of antigen in extracts of liver or spleen prepared in the same way.4. Protein fractions (;N-fractions') from various organs and tissues of pigs were obtained by the same methods used to prepare neurophysin from posterior pituitaries and were tested for antigenicity in reaction with neurophysin antibody. N-fractions from kidney, uterus, mammary gland and serum contained antigen while fractions from liver, spleen, brain and skeletal muscle did not react with the anti-neurophysin serum.