The present invention relates to peptides containing guanidine and halogenated biphenyl moieties of the formula (I), and to salts and solvates of each of these peptides and to processes for the preparation thereof, compositions containing them and the uses of such compounds. It has been found that the compounds have a high microbicide activity and are suited to combat resistant bacteria, such as Methicillin-resistant Staphylococcus aureus (MRSA) strains, at very low concentrations.