Carbon nanotubes are strong, flexible, conduct electrical current, and can be functionalized with different molecules, properties that may be useful in basic and applied neuroscience research. We report the first application of carbon nanotube technology to neuroscience research. Methods were developed for growing embryonic rat-brain neurons on multiwalled carbon nanotubes. On unmodified nanotubes, neurons extend only one or two neurites, which exhibit very few branches. In contrast, neurons grown on nanotubes coated with the bioactive molecule 4-hydroxynonenal elaborate multiple neurites, which exhibit extensive branching. These findings establish the feasability of using nanotubes as substrates for nerve cell growth and as probes of neuronal function at the nanometer scale.