The gene encoding SCG10 was originally isolated as a neuronal marker from neural crest derivatives, implying that this protein may contribute to fundamental neuronal properties. To examine the developmental change of SCG10 expression in brain, immunoblot analysis and in situ hybridization were performed in embryonic day 15 (E15), E19, postnatal day 0 (P0), P6, P14, P30 and P90 rat brains. The distribution of SCG10 mRNA was compared to those of its homologue, p19/stathmin, and the well-characterized growth-associated protein GAP-43. Overall expression of SCG10 in brain reached a peak at E19 and decreased gradually by P30 to the adult level. The expression pattern of SCG10 in E15 whole body was identical with that of GAP-43; both mRNAs were specifically detected in developing neuronal structures. p19/stathmin mRNA, on the other hand, showed widespread expression throughout the whole body. Expression patterns of the three mRNAs overlapped in many structures in the perinatal brain, yet each showed unique expression during postnatal development. For example, in the developing cerebellum, strong GAP-43 expression was found in the external granule cells, which are presumably extending parallel fibers, while SCG10 strongly hybridized in the internal granule cells which have reached their final position and begun dendrite outgrowth. The unique transient expression of p19/stathmin was found in the subventricular zone in the cortex, the white matter in the cerebellum, the optic nerve layer of the superior colliculus and the inner edge of the dentate granule layer in the hippocampus. Considering the timing, all of these areas are known to produce neurons or glia. This is consistent with the suggestion that p19/stathmin is related to differentiation. SCG10 may be a new member of growth-associated proteins and this protein may contribute to neurite extension in perinatal brain as does GAP-43. However, the differential expression between SCG10 and GAP-43 in later developmental stages suggests their diverse functions, which indicates these proteins may play different roles during postnatal brain development.