1. Hughes, J. et al. Nature 258, 577–579 (1975).
2. Li, H. L. & Chung, D. Proc. natn. Acad. Sci. U.S.A. 73, 1145–1148 (1976).
3. Guillemin, R., Ling, N. & Burgus, R. c. hebd. Séanc. Acad. Sci. Ser. D. 282, 783–785 (1976).
4. Bradbury, A. F., Feldberg, W. F., Smyth, D. G. & Snell, C. R. in Opiates and Endogenous Opioid Peptides (ed. H. W. Kosterlitz,) 9–17 (North-Holland, Amsterdam 1976).
5. Cox, B. M., Opheim, K. E., Teschemacher, H. & Goldstein, A. Life Sci. 16, 1777–1782 (1975).