AbstractThe coagulating gland of rodents, which is part of the prostatic complex, secretes components of semen. Although possessing some ultrastructural features of other exocrine glands, the mechanism of secretion by these cells has been problematic. In the present study the pathway, kinetics, and mode of secretion in the coagulating gland of the mouse were studied by light and electron microscope autoradiography at intervals between 10 minutes and 3 hours after injection of3H‐fucose. The majority of silver grains overlay the Golgi apparatus at the initial interval, but in addition, more than a third of the grains were associated with extremely distended cisternae of the rough endoplasmic reticulum. At later intervals, radioactivity of the Golgi apparatus and the endoplasmic reticulum declined, while labeling of secretory granules increased greatly. Luminal contents became labeled 1 hour after administration of precursor. The results indicate that the pathway for secretion of glycoproteins proceeds through the Golgi apparatus to secretory granules and the glandular lumen, as in many other cells. In particular, heavy labeling of secretory granules at later intervals indicates that merocrine secretion is the most likely mechanism in the coagulating gland. However, the unusual observation that a significant proportion of grains overlay the rough endoplasmic reticulum at the initial interval raises the possibility that some fucose is incorporated into glycoproteins in the endoplasmic reticulum, as has been reported for other cell types with similarly configured endoplasmic reticulu