Ageladine A is a marine natural product that can be used to fluorescently stain living tissues and cells. Its fluorescence is highly pH dependent with the highest intensities under acidic conditions. We have used ageladine A to stain acidic vesicles in cells and found the compound especially useful for tracking transport vesicles in cultured nerve cells. Inward as well as outward ionic currents appear not to be influenced by ageladine A at concentrations of 10 μM or less. Higher concentrations than 30 μM reduce whole cell voltage dependent outward currents whereas inward currents remain unchanged up to 100 μM ageladine A (PC12 cells). Incubation with ageladine A (10 μM) in cultured hippocampal neurons does not alter miniature excitatory postsynaptic currents (mEPCS) amplitudes, frequency, rise or decay times. Fast moving vesicles are stained the brightest, suggesting they are the most acidic and likely to be Golgi derived and endocytotic vesicles for the fast anterograde and retrograde transport of proteins and other compounds needing an acidic environment.