AbstractNishioka, R. S., Bern, H. A., Gunther, R. L.1980. Hormone‐carrier‐neurosecretory granule association in the urophysis of the gobyGillichthys mirabilis.(Department of Zoology and Cancer Research Laboratory, University of California, Berkeley, California, N.S.A.) —Acta zool.(Stockh.) 61(1): 29–38.The caudal neurosecretory system of the mudsucker,Gillichthys mirabilis, was investigated using continuous sucrose density gradient centrifugation, electron microscopy, polyacrylamide gel electrophoresis, and bioassay. A strong light‐scattering band near the 41 % sucrose concentration was shown to contain neurosecretory granules by electron microscopy and urotensin II activity by bioassay. Aliquots of this band were run in polyacrylamide gel electrophoresis and the selected regions of the gel containing those bands unique to urophysial tissue were cut out and eluted after the gel had been sliced longitudinally. The eluate from the region of the unique band (rf 0.46) gave the highest urotensin II bioassay activity when compared to adjacent areas. The remaining half of the gel was stained to confirm the localization of the unique bands. Gels made from regions adjacent to the 41 % sucrose concentration showed less stainability of the bands, and eluate of regions from its unique bands contained correspondingly less bi