Progressive loss of neuronal cytoarchitecture is a major event that precedes neuronal death, both in neural aging and in neurodegenerative diseases. Cytoskeleton in neurodegenerative diseases is characterized by hyperphosphorylated tau assembled in neurofibrillary tangles. Tau protein promotes microtubule enlargement and its hyperphosphorylation inhibits tubulin assembly. Okadaic acid (OA) causes oxidative stress, tau hyperphosphorylation, and altered cytoskeletal organization similar to those observed in neurons of patients with dementia. Since melatonin acts by both enlarging microtubules and as a free-radical scavenger, in this work we studied the effects of melatonin on altered cytoskeletal organization induced by OA in N1E-115 neuroblastoma cells. Optic microscopy, morphometric analysis, and tubulin immunofluorescence staining of neuroblastoma cells incubated with 50 nM OA showed an intact microtubule network following the neurite profile similar to that observed in the vehicle-incubated cells when melatonin was added to the incubation media 2 h before OA. The melatonin effects on altered cytoskeletal organization induced by OA were dose-dependent and were not abolished by luzindole, the mt(1) melatonin antagonist receptor. Also, increased lipid peroxidation and augmented apoptosis in N1E-115 cells incubated with 50 nM OA were prevented by melatonin. The results support the hypothesis that melatonin can be useful in the treatment of neurodegenerative diseases.