Nissl staining is a standard histological method for visualizing neurons in the brain and spinal cord. Composed of ribosomal RNA associated with the rough endoplasmic reticulum in neuronal perikarya and dendrites, the Nissl substance redistributes within the cell body in injured or regenerating neurons, providing a marker for the physiological state of the neuron. Our NeuroTrace 640/660 deep-red fluorescent Nissl stain is selective for the Nissl substance characteristic of neurons and provides more sensitivity than traditional histological dyes like toluidine blue or cresyl violet.