To provide a further reagent (antimicrobial peptide (AMP)) which is usable for treatment or prevention of a microbial infection.

The present invention relates to cyclic cationic peptides and their use in the treatment of microbial infections: the use of a cyclic peptide, or variant thereof, comprising amino acids represented by formula (I): ((X)₁(Y)_m)_n, wherein 1 and m are integers from 0 to 10 such that both 1 and m are not 0; n is an integer from 1 to 10; X and Y, which may be the same or different, are an amino acid selected from the group consisting of cationic amino acids, for use in the production of a medicament for treating a microbial infection.