A method for cleaning a medical or dental instrument comprising: (a) soaking the medical or dental instrument in an aqueous composition comprising i) from 0.001% w/w to 1% w/w of a protease, wherein the protease is subtilisin, and ii) from 0.001% w/w to 1% w/w of a peptide aldehyde protease stabilizer; (b) optionally washing the instrument with a liquid detergent composition; and (c) rinsing the instrument; wherein the peptide aldehyde protease stabilizer has the formula P-B 2 -B 1 -B 0 -H or a hydrosulfite adduct thereof having the formula P-B 2 -B 1 -N(H)-CHR-CHOH-SO 3 M, wherein i) H is hydrogen; ii) B 0 is a single amino acid residue with L- or D-configuration of the formula -NH-CH(R)-C(=O)-; iii) B 1 and B 2 are independently single amino acid residues; iv) R is independently selected from the group consisting of C 1-6 alkyl, C 6-10 aryl or C 7-10 arylalkyl optionally substituted with one or more, identical or different, substituents R'; v) R' is independently selected from the group consisting of halogen, -OH, -OR", -SH, -SR", - NH 2 , -NHR", -NR" 2 , -CO 2 H, -CONH 2 , -CONHR", -CONR" 2 , -NHC(=N)NH 2 ; vi) R" is a C 1-6 alkyl group; vii) P is an N-terminal protection group; and viii) M is H or an alkali metal, preferably Na or K. (a) soaking the medical or dental instrument in an aqueous composition comprising i) from 0.001% w/w to 1% w/w of a protease, wherein the protease is subtilisin, and ii) from 0.001% w/w to 1% w/w of a peptide aldehyde protease stabilizer; i) from 0.001% w/w to 1% w/w of a protease, wherein the protease is subtilisin, and ii) from 0.001% w/w to 1% w/w of a peptide aldehyde protease stabilizer; (b) optionally washing the instrument with a liquid detergent composition; and (c) rinsing the instrument; wherein the peptide aldehyde protease stabilizer has the formula P-B 2 -B 1 -B 0 -H or a hydrosulfite adduct thereof having the formula P-B 2 -B 1 -N(H)-CHR-CHOH-SO 3 M, wherein i) H is hydrogen; ii) B 0 is a single amino acid residue with L- or D-configuration of the formula -NH-CH(R)-C(=O)-; iii) B 1 and B 2 are independently single amino acid residues; iv) R is independently selected from the group consisting of C 1-6 alkyl, C 6-10 aryl or C 7-10 arylalkyl optionally substituted with one or more, identical or different, substituents R'; v) R' is independently selected from the group consisting of halogen, -OH, -OR", -SH, -SR", - NH 2 , -NHR", -NR" 2 , -CO 2 H, -CONH 2 , -CONHR", -CONR" 2 , -NHC(=N)NH 2 ; vi) R" is a C 1-6 alkyl group; vii) P is an N-terminal protection group; and viii) M is H or an alkali metal, preferably Na or K. i) H is hydrogen; ii) B 0 is a single amino acid residue with L- or D-configuration of the formula -NH-CH(R)-C(=O)-; iii) B 1 and B 2 are independently single amino acid residues; iv) R is independently selected from the group consisting of C 1-6 alkyl, C 6-10 aryl or C 7-10 arylalkyl optionally substituted with one or more, identical or different, substituents R'; v) R' is independently selected from the group consisting of halogen, -OH, -OR", -SH, -SR", - NH 2 , -NHR", -NR" 2 , -CO 2 H, -CONH 2 , -CONHR", -CONR" 2 , -NHC(=N)NH 2 ; vi) R" is a C 1-6 alkyl group; vii) P is an N-terminal protection group; and viii) M is H or an alkali metal, preferably Na or K. <EOS>