Kinesin is a microtubule-based motor protein involved in intracellular organelle transport. Neurons are characterized by the presence of at least two isoforms of conventional kinesin: ubiquitous kinesin, expressed in all cells and tissues, and neuronal kinesin, whose pattern of expression is confined to neuronal cells. In order to investigate whether the two kinesin motors, which are encoded by different genes, may play distinct biological roles in neurons, we studied their expression during neuronal differentiation. Human neuroblastoma SH-SY5Y and IMR32 cells and rat phaeochromocytoma PC12 cells were used as an in vitro system for neuronal differentiation and were induced to differentiate in the presence of retinoic acid, a combination of dibutyryl cAMP and 5-bromodeoxyuridine, and nerve growth factor respectively. The expression level of each kinesin isoform was evaluated by quantitative immunoblot before and after pharmacological treatment. We found that in all cell types the expression level of neuronal kinesin, but not of ubiquitous kinesin, is stimulated during differentiation. In particular, SH-SY5Y cells show a 4.5-fold, IMR32 cells a 3-fold and PC12 cells a 7-fold increase in the level of expression of neuronal kinesin. By Northern blot analysis we found that the selective increase in the expression of neuronal kinesin is paralleled by an increase in its mRNA, indicating that there is a transcriptional control of the expression of this kinesin isoform during differentiation of neuroblastoma and PC12 cells. Our results suggest that these cells represent an adequate model to study the function of conventional kinesin and its isoforms.