Ageladine A stems from sponges of the genus Agelas and belongs to the chemical group of brominated pyrrole imidazole alkaloids, which have been shown to possess a high pharmacological potential. Ageladine A can be used as a pH -sensitive dye in living cells, tissues and whole organisms with apparently little side effects. Especially whole animal staining in transparent marine animals showed to be successful. The major change and increase of fluorescence in the blue to green wavelength range can be observed between 8 and 5 pH units. Dying or energy -deficient cells are increasingly unable to regulate intracellular pH values due to lower transport rates and mitochondrial dysfunction, which leads to acidification of the cytosol of at least 0.5 to 1 pH units. Ageladine A shows its best sensitivity range in the most relevant pH range between pH 7 and 6 and is therefore useful for detection of small irregularities in the cellular pH homeostasis. We used PC12 cells, intestinal cells and neuronal cells from Drosophila as well as nematode eggs to demonstrate the strong fluorescence in stressed or dying cells.