Disclosed are thrombin peptide derivatives comprising a polypeptide having the amino acid sequence SEQ ID NO. 2: Arg-Gly-Asp-Ala-Xaa-Glu-Gly-Asp-Ser-Gly-Gly-Pro-Phe-Val, or a C-terminal truncated fragment of the polypeptide having at least six amino acids. Xaa is alanine, glycine, serine, or an S-protected cysteine. Zero, one, two, or three amino acids in the polypeptide or polypeptide fragment differ from the corresponding position of SEQ ID NO. 2. Also disclosed are methods of treating a subject in need of treatment with a thrombin receptor agonist. The methods comprise the step of administering an effective amount of the thrombin peptide derivative described above.