The present invention provides peptidic TGF-β antagonists capable of inhibiting TGF-β signaling and disrupting the biochemical events that promote fibrosis and the epithelial-mesenchymal transition. The peptidic TGF-β antagonist may contain from 11 to 28 amino acid residues (for instance, may consist of from 12 to 16 amino acid residues) and may have the following structure (II): NH2′ ETWIWLDTNMG-Xaa1-Y′COOH (II) wherein Xaa1 is any amino acid and Y is a peptide having from 0 to 9 amino acids. The peptidic TGF-β antagonists can advantageously be used for the prevention, treatment, and/or alleviation of the symptoms of a condition associated with an increase in TGF-β activity, including fibrosis (such as fibrosis of the skin, liver, lungs, and heart, among others) and cancer (including various carcinomas, such as squamous cell carcinoma, sarcomas, and metastatic cancers).