The fine-structural changes in the secretory pathways were studied in the rat prostatic epithelial cells after castration. Alterations were first noticed in the rough-surfaced endoplasmic reticulum (on day 2). A gradual reduction in the number of Golgi-associated, smooth-surfaced vesicles, vacuoles with granular content (“condensing vacuoles”), and secretory granules occurred from day 3 onward. The vacuoles with granular content appeared to be replaced in part by “empty” vacuoles. The Golgi apparatus proper showed decreased size on days 3–5, and later seemed to lose its structural polarity in the cells. Apparent acid phosphatase activity was present in the Golgi apparatus (cisternae and some vesicles), vacuoles (“empty” and with granular content) associated with the Golgi apparatus, secretory granules, apical “empty” vacuoles, lysosomes, and the alveolar lumen at intervals up to day 20 after castration. The observations suggest (a) that the occurrence of small smooth-surfaced vesicles at the periphery of the Golgi complex, condensing vacuoles, and secretory granules is dependent on the continuous production of the normal secretory product by the rough-surfaced endoplasmic reticulum; (b) that cessation of major androgenic hormone action results in quantitative and morphologic changes in the secretory product while the pathways for the intracellular transport are essentially unaltered; (c) that the reduction in size of the Golgi apparatus is relatively slow and gradual and is unrelated to autophagy; and (d) that the loss of polarity of the Golgi apparatus is due to the combined effects of diminished function in secretion and retained function in, for example, random lysosome production.