Many new peptide therapeutics are increasingly making their way to rapid and successful clinical application. In fact, some naturally derived peptide chains were used as effective drugs for several years. With the emergence of very large libraries of peptides with high biological properties, it is expected that several potential candidates will be introduced to the list of under-development peptides, introducing new drug-administration strategies derived from polypeptide chains and improvements in the purification half-life in vivo. Despite remaining potential hurdles, peptide therapies are poised to play an important role in treating diseases ranging from Alzheimer's disease to cancer.