The invention relates to the use of a peptide mixture comprising peptides with a molecular weight from 1000 to 5000 Daltons for the prevention and/or treatment of tumour diseases, of diseases which are associated with a development disorder of the immune system, of diseases of the immune system, of autoimmune reactions, of allergies and of inflammation in man, a protein component which contains such a peptide mixture and a formula food containing this peptide mixture. The peptides are preferably obtained from non-human proteins suitable for nutritional purposes, in particular by the enzymatic or hydrolytic cleavage of these proteins.