As observed autoradiographically in the cartilage of embryonic rats, radiosulfate is bound and concentrated only in vesicles of the juxtanuclear Golgi apparatus of secreting chondrocytes within 3 minutes of its presentation. From this area, vacuoles migrate peripherally and lodge in the subcortex; their sulfated contents are thence discharged via stomata to the extracellular matrix. The label, apparently often associated with microvesicles at 10 and 20 minutes, is subsequently localized in the dense contents of the larger vacuoles. Bound radiosulfate is not detectable in other organelles. It is concluded that the vesicular component of the Golgi apparatus is the actual site of sulfation. Intracellular hyaluronidase-sensitive metachromatic granules are found chiefly at the cell periphery or mantle, rarely juxtanuclear in the main Golgi zone.