Abstract: There is disclosed a series of novel cyclic tetrapeptides related to somatostatin. The compounds have surprisingly been found to have the activity of increasing blood glucose when administered. The compounds are prepared using the solid phase or mixed anhydride synthesis methods and compositions and methods utilizing the novel compounds are also disclosed.

Abstract: Antibiotic A-21978C complexes, in particular the A-21978C complex, comprising microbiologically active, related factors, C.sub.0, C.sub.1, C.sub.2, C.sub.3, C.sub.4, and C.sub.5. A-21978 complex and A-21978C complex are produced by submerged aerobic fermentation of Streptomyces roseosporus NRRL 11379. The individual A-21978C factors are separated and isolated by chromatography. The A-21978 and A-21978C complexes, the A-21978C factors, and pharmaceutically acceptable salts thereof are antibacterial agents and improve growth promotion in poultry.