Dysfunction of the microtubule system is emerging as a contributing factor in a number of neurodegenerative diseases. Looking for the potential role played by the microtubule cytoskeleton in neuron degeneration underlying Parkinson's disease (PD), we investigate the influence of the parkinsonism producing neurotoxin 1-methyl-4-phenylpyridinium (MPP+) on microtubule dynamics. We find that it acts as a strong catastrophe promoter causing a decrease of the average length of microtubules assembled from purified tubulin. We also find that it reduces the number of microtubules nucleated from purified centrosomes. Finally, binding assays demonstrate that the neurotoxin binds specifically to tubulin in the microtubule lattice in a close to stoichiometric manner. This paper provides the first evidence that dynamic instability of microtubules is specifically affected by MPP+ and suggests that it could play a role in neuronal cell death underlying PD.