Based on an approach to design outlined in (ref. 34 of my C. V.-Towards the Design of Neurohypophysial Peptides Possessing Selectively Enhanced and Inhibitory Properties, M. Manning, et al. In: Peptides Chem., Structure and Biology, Ann Arbor Science, 1975, p. 737), it is proposed to meet the following objectives: 1. To continue study of the structural alterations of arginine vasopressin (AVP) which regulate (a) antidiuretic specificity and (b) duration of action. 2. To complete the synthesis and pharmacological characterization of the known neurohypophysial peptides. 3. To design and synthesize selectively acting antagonists of the (a) oxytocic and (b) antidiuretic responses of oxytocin and vasopressin respectively. 4. To design and synthesize a selectively acting potent oxytocic agent devoid of antidiuretic activity. 5. To design and synthesize selectively acting regional vasopressor agents. 6. To continue to provide other investigators with samples of synthetic peptides for their independent investigations. BIBLIOGRAPHIC REFERENCES: Towards the Design of Neurohypophysial Peptides Possessing Selectively Enhanced and Inhibitory Properties, M. Manning, J. Lowbridge and W.H. Sawyer, In: Peptides Chemistry, Structure and Biology, R. Walter and J. Meienhofer (eds.) Ann Arbor Science, (1975) p. 737.