Abstract: The neurotropic effect of the distal stump of transected sciatic nerve on regenerating neurites emerging from the proximal stump was investigated in rats by the co-culture of excised dorsal root ganglia and segments of degenerated and nondegenerated sciatic nerves.In all cultures,neurites from the ganglion extended directly towards the degenerated distal stump and not towards the undegenerated nerve segment.Analysis of the supernatants of nerve homogenate by native polyacrylamidegel electrophoresis demonstrated that 235 and 18 kDa proteins were upregul ated in the degenerated distal stumps and that 90 and 65 kDa special proteins were expressed by these stumps but not by normal nerve.Placement of the individual protein strips in dissociated cultures of dorsal root ganglion cells showed that the 90 kDa strips possessed strong neurotropic activity.Neurons survived selectively on these strips and outgrowing neurites elongated on the strips paralled to the direction of the band.It is concluded that these bands contain chemotropic substances,the nature of which requires further investigation.