Professor Philip S. Portoghese, University of Minnesota Letter, dated 6 December 1976, from Portoghese to Kosterlitz, saying that he was happy to find that Kosterlitz 'had suggested the possibility of a family of receptors based on rank - order potencies of different series of opiates' in the latest installment on the status of enkephalin in 'Nature' 262 (1976). Portoghese writes, 'As we employed this approach in 1965 and in subsequent publications I am happy that you believe there is validity to this concept'. Letter is enclosed with a photocopy of Pfilh C. Portoghesl [Philip S. Portoghese], 'A New Concept on the Mode of Interaction of Narcotic Analgesics with Receptors' reprinted from 'Journal of Medicinal Chemistry 8 (1965), 609 - 615. Includes a reply letter from Kosterlitz, dated 17 December 1976, which mentions 'Our approach is based on the use of four different assay systems, namely the inhibition of the contractions of (1) the guinea - pig ileum and (2) the mouse vas deferens, and the inhibition of binding of (3) {'3'H} - leucine - enkephalin and (4) {'3' H} - naloxone'. Letter, dated 23 November 1987, from Kosterlitz to Portoghese, asking to be sent some samples of BNI and nor - BNI. Kosterlitz writes, 'We have for some time been concerned with the interaction of k - ligands with their receptors, as for instance dynorphin A (1 - 9) and the cerebellum of the guinea - pig'. Includes a reply letter from Portoghese, dated 30 December 1987. Correspondence relates to some of Kosterlitz's & colleagues', and Portoghese's respective scientific results and the sending of other scientific samples. Letter, dated 7 April 1988, from Kosterlitz, congratulates Portoghese on 'obtaining these selective opioid antagonists'. Letter, dated 3 June 1988, from Kosterlitz to Portoghese, encloses the results Stewart Paterson, Alistair Corbett and Kosterlitz found for 'Naltrindole and methyl - NTI'. The correspondence begins in December 1976. There are gaps in the correspondence: between December 1976 and November 1987; January - April 1988, and April - June 1988. 1976 - 1988