The board and long term objective is to study the structure and conformation details of cyclic peptides in the crystalline state using x-ray crystallographic techniques. Many biologically active naturally occuring substances like hormones, toxins, antibiotics and ion transport regulators are or contain cyclic peptide moieties. Synthetic analogs of naturally occuring peptides can be easily synthesized and their conformation and biological activity studied. The conformation of a molecule is intimately related to its biological activity. The study of the conformation of cyclic peptides crystallized under different conditions and comparison of the details with those obtained from other methods could be very valuable in determining the bioactive conformation. The process of cyclization reduces the number of possible conformations available for the linear counterpart. The conformational restrictions imposed by cyclization on the peptide geometry make cyclic peptides excellent models for better understanding the basic principles that regulate peptide conformation and the fundamental conformational properties of proteins. Many of the cyclic molecules also interact with biologically important metal ions. These sever as good models for better understanding the mechanism of ion transfer across the biological membranes and understanding the interaction of these ions with peptides and proteins. In this project, the examination of the structure and conformation of a few synthetic cyclic peptides that are useful as analogs for biologically active molecules using x-ray crystallographic techniques is planned. The conformational details obtained by these studies when compared with those obtained from spectroscopic methods may yield information regarding internal mobility of peptide bond. The conformational information may be of use in designing cyclic peptides to carry out specific biological functions such as ions carriers, antibiotics or other useful drugs.