We investigated the effects of microtubule inhibitors, taxol and colchicine, on the axonal branching and elongation in cultured rat hippocampal neurons. Taxol (50 nM) did not affect the morphology of neurons cultured under the control conditions, but significantly reduced the axonal branching stimulated by basic fibroblast growth factor. The axonal elongation stimulated by astrocyte-conditioned medium was not affected by the same concentration of taxol. Colchicine (10 nM) showed similar effects as taxol. These results suggest that microtubules play more important roles in axonal branching than in axonal elongation.