Light and electron microscopic studies of the adrenal medulla of golden hamsters (Mesocricetus auratus) indicates that the chromaffin cells are arranged in hitherto undescribed irregular follicles surrounded by thin-walled blood vessels. Each follicle is generally one cell thick with a lumen of variable size and shape, which contains finely granulated materials, nerve endings and chromaffin cell processes. Chromaffin cells are polarized; basal regions, containing the nuclei, about on the follicular cavity, and the apical areas are in close proximity to blood vessels. In the central portion of the organ, follicles contain only adrenaline cells while at the periphery “mixed follicles” occur which have both adrenaline and noradrenaline cell types. Occasional follicles with only noradrenaline cells are found in this area also. These findings have been compared with previous observations. The possible function of the follicular cavities has been discussed briefly.