1-Aminodecylidene bis-phosphonic acid is a potent inhibitor of acid sphingomyelinase (IC50 = 20 nM). It is selective for acid sphingomyelinase over neutral sphingomyelinase (IC50 = >100 μM). 1-Aminodecylidene bis-phosphonic acid completely inhibits apoptosis induced by dexamethasone in HepG2 cells.