A KOH-collagenase or simple KOH digestion method was employed for scanning electron microscope (SEM) studies of elastin components in the rat thoracic aorta, mouse urinary bladder, and human ductus deferens. Immersion of the fixed tissues in 30% KOH solution for 8-10 min at 60 degrees C, with or without subsequent collagenase treatment, successfully removed collagen fibrils and basal laminae while leaving cellular and elastin elements unchanged at their original shapes and locations. The internal elastic lamina of the rat aorta appeared as a solid sheet formed by elastin fibrils 0.1-0.2 microns thick, while the medial elastic laminae were more fibrous because of the presence of numerous fine elastin fibers on their surface. Adventitial elastin fibers were of a cord-like shape complicatedly entangled among the adventitial fibroblasts. These fibers were seen as bundles of fibrils 0.1-0.2 microns thick. In the mouse urinary bladder, elastin formed a thin lace-like sheet just beneath the serosal covering of the peritoneum. This sheet was composed of small bundles of fine (0.1-0.2 microns thick) fibrils. The external connective tissue of the human ductus deferens was made up of a three-dimensional loose network of elastin fibers 0.1-1.5 microns thick. These fibers also appeared as bundles of the fine fibrils. These findings indicate that the present method is useful for SEM studies of elastin as well as cellular components in various tissues and organs. This study also maintains that elastin fibers and laminae are basically composed of unit fibrils of 0.1-0.2 microns thickness. As elastin components are arranged specific to individual organs and tissues, it is reasonable that these components are concerned in the characteristic mechanical properties of these tissues and organs.