Neuro-DiI uniformly dissolved in vegetable oil in a formulation optimized for microinjection. Neuro-DiI was developed at Biotium as an alternative to the widely used fluorescent membrane probe DiI. Neuro-DiI has structural features that may make the probe diffuse faster than DiI on cell membranes and also may result in a more stable labeling. Neuro-DiI has nearly identical absorption and emission wavelengths to those of DiI.