Goosefish islet secretion granules were isolated from sucrose homogenates by centrifugation. The morphology of the fractions was determined by electron microscopy. Studies on the stability of the secretion granules revealed them to be sensitive to pH and deoxycholate. The secretion granule proteins were subjected to electrophoresis in polyacrylamide gels, and the resultant bands were characterized by a number of stains and by immunoassay of insulin. These procedures showed that the granule fraction had a heterogeneous configuration consisting of lipid, carbohydrate and protein. One band containing much of the insulin activity did not show the ability to stain with aldehyde fuchsin, possibly indicating a different character of insulin.