A fraction rich in secretory granules was prepared from the pyloric caeca of Asterias amurensis by sucrose density gradient centrifugation. The freshly prepared fraction exhibited no casein-hydrolyzing activity, but showed nine times as much specific activity as that of tissue homogenates after incubation at 37 degrees C for thirty minutes. Electron microscopy showed that the secretory granules were membrane-bound granules measuring 0.5-2.0 mu in diameter and contained dense and/or light amorphous substances.