4-(2-Aminoethyl)benzenesulfonyl fluoride hydrochloride (AEBSF) is an irreversible serine protease inhibitor. Inhibition constants are similar to those of phenylmethanesulfonyl fluoride (PMSF) and diisopropylfluorophosphate (DFP). AEBSF has been shown to inhibit trypsin, chymotrypsin, plasmin kallikrein, and thrombin. As an alternative to PMSF and DFP, AEBSF offers lower toxicity, improved solubility in water, and improved stability in aqueous solutions. AEBSF can be used in cell culture in concentrations of up to 0.25 mM.