Abstract The structure and conformation of the cyclodipeptide, cyclo (Tyrosyl-Prolyl), cyclo (Tyr-Pro) have been investigated with X-ray crystallographic and spectroscopic methods. Two conformations of cyclo (Tyr-Pro) crystallized in the space group P 2 1 2 1 2 with cell dimensions a= 11.890 (3), b= 12.057 (1), c= 18.528 (4). Both these conformations are uncommon for cyclodipeptides containing a proline residue. The tyrosyl side chains of ...