Pepstatin (Pepstatin A) is a specific, orally active aspartic protease inhibitor produced by actinomycetes, with IC50s of 4.5 nM, 6.2 nM, 150 nM, 290 nM, 520 nM and 260 nM for hemoglobin-pepsin, hemoglobin-proctase, casein-pepsin, casein-proctase, casein-acid protease and hemoglobin-acid protease, respectively. Pepstatin also inhibits HIV protease.