Paraffin sections of 95% ethanol-fixed uterine cervices from adult, cycling rats and from human patients undergoing elective hysterectomy were immunostained by the peroxidase-antiperoxidase technique after exposure to antisera against fibronectin. Light microscopic study of uterine cervical stroma from both species showed an irregular distribution of fibronectin between compactly arranged collagenous fibers and a more uniform deposition around scattered bundles of smooth muscle fibers. In loosely arranged areas of stromal collagen, fibronectin was found in a filamentous, occasionally punctate, distribution. There was moderate to heavy staining with immunoperoxidase for fibronectin in the regions of the basement membrane underlying cervical epithelia and in the connective tissue stroma immediately subjacent to the basement membrane. Fibronectin was also present in the walls of most blood vessels and in the connective tissue investments of peripheral nerve fascicles. These findings suggest that fibronectin may be another component of extracellular matrix in the uterine cervical wall of nongravid human subjects and rats in addition to collagen and glycosaminoglycans.