Chromaffin cells of the adrenal medulla contain prominent arrays of microtubules and microfilaments. One population of microtubules radiates from the cytocentrum and permeates the areas of the cytoplasm containing chromaffin granules; the other population of microtubules forms a subplasmalemmal network together with actin-like microfilaments. Hence, the cytoskeletal elements in chromaffin cells are strategically located to participate in the mobility of chromaffin granules to the cell surface and to regulate access of the granules to the plasma membrane during exocytosis. Agents which effect the integrity of the cytoskeleton clearly affect the secretory process in a manner which indicates that the microtubules and microfilaments play an active role in the release process.