The study of neuronal connectivity requires the ability to trace axons from the neuronal cell body to its axon terminal (anterograde tracing) and from the terminal back to the soma (retrograde tracing). Such neuroanatomical tracing is frequently used to identify neurons on the basis of their pre- or postsynaptic connections. Neuroanatomical tracing has become particularly important in nervous system regeneration and repair, allowing investigators to follow the axon projections of newly born, transplanted, or axotomized neurons in lesioned or neurodegenerative environments. To allow further study of neurons identified and labeled in this way, it is particularly important that tracers are compatible with other tissue processing such as immunocytochemistry. Fluoro-Gold (Fluorochrome Inc., Denver CO) is one such highly flexible fluorescent retrograde marker commonly used for neuronal labeling and neuroanatomical tracing.