Using the slice culture system for 9-day-old rat cerebellum, roles of nitric oxide (NO) in the cerebellar cortical development were examined. Granule cell migration was inhibited by N-nitro-L-arginine (L-NNA) and by haemoglobin (Hb), but not by N-nitro-D-arginine (D-NNA), added to the culture medium, showing that NO-mediated transmission is involved in some process for granule cell migration. Furthermore, immunohistochemical analysis revealed that the cessation of granule cell proliferation and the differentiation of Bergmann glia were inhibited in the presence of L-NNA and Hb. These results suggest that endogenous NO can be a signal for the differentiation of granule cells and Bergmann glia in cerebellar cortical development.