The transport properties of the lectin Phaseolus vulgaris leucoagglutinin (PHA-L) were tested in the frog central nervous system. After delivery of the lectin to the lower brainstem by iontophoresis, stained axons and axon terminals, as well as neurons with richly arborizing dendrites, were observed indifferent regions of the brain and spinal cord even far away from the site of application. The large number and the Golgi-like appearance of labeled neurons situated rostral and caudal to the site of PHA-L deposit indicate that PHA-L is transported equally in both the anterograde and the retrograde direction in the central nervous system of the frog. This is in contrast with the mammalian nervous system, in which PHA-L is transported predominantly in the anterograde direction and the retrograde transport is poor.