Abstract: Methods for treating treating fibrosis in a mammal are described. An antifibrotic effective amount of a peptide having the formula f-Met-Leu-X where X is selected from the group consisting of Tyr, Tyr-Phe, Phe-Phe and Phe-Tyr is administered to the mammal. The fibrosis may be due to pathological changes resulting, e.g., from pulmonary fibrosis, atherosclerosis, cirrhosis, glomerulosclerosis, chronic pancreatitus, coronary artery disease (such as caused by infection by bacterium Chlamydia pneumoniae), trauma or surgical procedures.