A cocktail consisting of five protease inhibitors useful for the inhibition of aspartic, cysteine, serine, metalloproteases and aminopeptidases. Each vial should be reconstituted with 1 ml DMSO and 4 ml H₂O to obtain a 5 ml stock solution. This protease inhibitor cocktail is recommended for use with bacterial cell extracts (except in case of use in metal ion chromatography). One set is sufficient for about 20 grams of cells.