The ciliary processes (CPs) in the rat were investigated for the presence of neuropeptide Y (NPY)-like immunoreactivity and for histofluorescence indicating catecholamine (CAM)-ergic innervation in the rat, rabbit and cynomolgus monkey. Special attention was paid to those CP vessel segments which in previous studies showed distinct reactions on application of CAM or NPY, and on the respective sections of the CP epithelium. In the rat and cynomolgus monkey most CAM-ergic nerve fibers concentrated along the terminal arterioles and the epithelium of the anteriormost portion of the major CPs. In comparison, the rabbit displayed most intense CAM-ergic innervation along the terminal arterioles and the epithelium of both the iridial processes and the anterior portion of the major CPs. The NPY-ergic nerve fibers built up a dense subepithelial nervous plexus in the anterior portion of the rat CPs, diminishing towards the posterior CPs. Also, many NPY-ergic fibers were found along the terminal arterioles of the anterior CPs. The findings demonstrate that CAM- and NPY-ergic nerve fibers preferentially supply vasculature and epithelium of the anterior ciliary processes, suggesting a crucial function of these structures for the precise regulation of aqueous humor formation.