Thin varicose centrifugal visual fibers, between 30-45 in number and displaying cGnRH-1 immunoreactivity, were identified in Crocodylus niloticus. Approximately 80% of these fibers were also FMRF-amide-like immunoreactive. The cGnRH-1 fibers extended from the preoptic region to the retina where they appeared to terminate in the external portion of the inner plexiform layer. The location of their neurons of origin could not be determined precisely following the intraocular injection of the retrograde axonal tracer RITC. Nevertheless, the presence of cGnRH-I-immunoreactive neurons exclusively within the complex comprising the terminal nerve and the septo-preoptic region, and of several retinopetal fibers labelled retrogradely with the axonal tracer at the septo-preoptic junction, indicates that the cGnRH-immunoreactive centrifugal visual system originates from within this complex. (c) 2005 Elsevier B.V. All rights reserved.