Fibers labelled with antibody to the growth associated protein (GAP-43) were observed as early as 4 gestational weeks (g.w.) in the nervous system of human embryos. At 6 g.w. these fibers could be traced throughout the brainstem and the diencephalon. None of the immunolabeled fibers entered the telencephalic wall at that point, but 2 weeks later at 8 g.w., GAP-43 positive fibers were observed below the newly formed cortical plate of the cerebral cortex. GAP-43 positive fiber bundles had the same distribution as those previously labeled with tyrosine hydroxylase antibodies at the same age. These results strongly suggest that this growth associated protein is localized in the early growing dopaminergic fibers.