An exogenous drug, benzyloxycarbonyl-Leucyl-Leucyl-Leucinal (Z-LLL-H) stimulates neurite outgrowth of PC12 cells. In this study, we observed the localization of a fluorescent peptidylaldehyde (Dns-LLL-H) in the cells by using fluorescence microscopy. Dns-LLL-H induced neurite outgrowth at the concentration of 10nM as well as Z-LLL-H. It was taken up within 10min after treatment and was concentrated spottily at the cell bodies, neurites and growth cones, but not at the nuclei and filopodia. These results suggest that Dns-LLL-H is localized at organelles of PC12 cells such as mitochondria and stimulates neurite outgrowth.