Bafilomycin A1 (BafA1) is a specific and reversible inhibitor of vacuolar H+-ATPase (V-ATPase) with IC50 values of 4-400 nmol/mg. Bafilomycin A1, a macrolide antibiotic, is also used as an autophagy inhibitor at the late stage. Bafilomycin A1 blocks autophagosome-lysosome fusion and inhibits acidification and protein degradation in lysosomes of cultured cells. Bafilomycin A1 induces apoptosis.