By means of immunocytochemistry with a battery of specific antibodies, we describe the expression of the collagen IV chain produced by the gene DCg1 during the two phases of Drosophila neurogenesis. DgC1 was not expressed in neuronal tissues as shown by in situ hybridization, but the onset of its expression in cells of mesodermal origin was concomitant with the appearance of collagen IV on early axon pathways and peripheral nerve roots in the embryonic developing CNS. A similar situation was found during imaginal CNS development at metamorphosis, when collagen IV immunoreactivity was detected on centrifugal and centripetal nerve pathways, and specially on retinula axons that develop from the eye imaginal disc towards the lamina anlage in the brain optic lobe. Our results strongly suggest that collagen IV could be involved, together with other informative molecules of basement membranes, in a dynamic process of cell-matrix interactions during the establishment of initial axon pathways and neurite outgrowth in vivo.