Lysosomes are subcellular organelles with acidic interiors (pH 3.5-5), containing enzymes that break down macromolecules and intracellular waste. Controlled release of lysosomal contents incurs programmed cell death (apoptosis), and may be regulated by lysosomotropic detergents (LDs), which are weakly basic amphiphiles. We study the synthetic LD O-methyl-serine dodecylamide hydrochloride (MSDH), in both model membranes and in cells, to clarify the permabilization mechanism, for which the pH difference between lysosome and cytosol is believed to be important. Cell studies show that MSDH cause apoptosis through lysosomal membrane permeabilization. A strong pH-dependence on MSDH aggregation and interaction with lipids has been confirmed by DLS and vesicle leakage assays. We ask for beamtime to investigate the the effects of MSDH on model lysosomal membranes under different conditions.