This invention relates to the use of an antagonist of a G protein-coupled receptor in the prevention and/or treatment of fibrosis, such as the treatment of fibrosis associated with myocardial infarction or diabetes or certain pulmonary conditions. In a preferred embodiment, the antagonist is a C5a receptor antagonist, more preferably a cyclic peptide antagonist of the C5a receptor. In particular, the invention provides a method of prevention, treatment or alleviation of a fibrotic condition, comprising the step of administering an effective amount of an antagonist of a G protein-coupled receptor to a subject in need of such treatment.