1. 1. Klein, J. The Natural History of the Histocompatibility Complex (Wiley, New York, 1986). 2. Duncan, W. R., Wakeland, E. K. & Klein, J. Immunogenetics 9, 261–272 (1979). 3. Klein, J. in Histocompatibility Antigens: Structure and Function. Receptors and Recognition, Series B. (eds Parham, P. & Strominger, J.) 221–239 (Chapman and Hall, London, 1982). 4. Van Rood, J. J., Van Leeuwen, A. & Van Santen, M. C. T. Nature 226, 366–367 (1970). 5. Vincent, C. & Revillard, J. P. Transplant Proc. 11, 1301–1302 (1979). 6. Callahan, G. N., Ferrone, S., Allison, J. P. & Reisfeld, R. A. Transplantation 20, 431–433 (1975). 7. Callahan, G. N., Ferrone, S., Penlik, M. D., Reisfeld, R. A. & Klein, J. /. Immun. 117, 1351–1355 (1976). 8. Zimmerman, F. A. el al. Transplant. Proc. 11, 571–577 (1979). 9. Diamond, A. D. et al. Eur. J. Immun. 14, 405–412 (1984). 10. Hart, D. N. J. & Fabre, J. W. Transplant. Proc. 13, 1329–1332 (1981). 11. Roser, B. & Dorsch, S. E. Immunol. Rev. 46, 55–86 (1979). 12. Scatchard, G. Ann. N.Y. Acad. Sci. 51, 660–672 (1949). 13. Ekins, R. P. Br. med. Bull. 30, 3–11 (1974). 14. Sundberg, H., Doving, K., Novikov, S. & Ursin, H. Behavioural and Neural Biology 34, 113–119 (1982). 15. Butcher, G. W. & Howard, J. C. Handbook of Experimental Immunology, 4th edn (ed. Weir, D. M.) 101.1–101.18 (Blackwell, Oxford, 1986). 16. Brown, R. E. & Macdonald, D. W. (eds) Social Odours in Mammals (Oxford University Press, 1985). 17. Brown, R. E. Advances in the Study of Behaviour 10, 103–162 (1979). 18. Beauchamp, G. K., Yamazaki, K. & Boyse, E. A. Sci. Am. 253, 66–72 (1985). 19. Yamazaki, K. et al. J. exp. Med. 144, 1324–1335 (1976). 20. Bruce, H. M. Nature 1284, 105 (1959). 21. Dominic, C. J. /. Reprod. Pert. 8, 266–267 (1964). 22. Yamazaki, K. et al. Science 221, 186–187 (1983). 23. Yamazaki, K. et al. Proc. natn. Acad. Sci. U.S.A. 83, 740–741 (1986). 24. Wysocki, C. J., Wellington, J. L. & Beauchamp, G. K. Science 207, 781–782 (1980). 25. Johns, M. A., Feder, H. H., Komisaruk, B. R. & Mayer, A. D. Nature 272, 446–447 (1978). 26. Yamazaki, K. et al. J. exp. Med. 150, 755–760 (1979). 27. Townsend, A. R. M., Bastin, J., Gould, K. & Brownlee, G. G. Nature 324, 575–577 (1986). 28. Maryanski, J. L., Pola, P., Corradin, G., Jordan, B. R. & Cerottini, J.–C. Nature 324, 578–579 (1986). 29. Bevan, M. J. & Fink, P. J. Immun. Rev. 42, 3–19 (1978). 30. Zinkernagel, R. M. & Doherty, P. C. Adv. Immun. 27, 51–177 (1979). 31. Schwende, F. J., Jorgenson, J. W. & Novotny, M. J. chem. Ecol. 10, 1603–1615 (1984). 32. Kirk, R. E. Experimental Design: Procedures for the Behavioural Sciences (Brooks/Cole, Belmont, California, 1968). 33. Brown, R. E., Singh, P. B. & Roser, B. J. Physiology and Behaviour (Pergamon, Oxford, in the press). 34. Ford, W. L. in Handbook of Experimental Immunology (ed. Weir, D. M.) 23.1–23.22 (Blackwell, Oxford, 1978). 35. Parham, P. J. biol. Chem. 254, 8709–8712 (1979). 36. Laemmli, V. K. Nature 227, 680–685 (1970). 37. Stephenson, S. P. Livingstone, A. M., Butcher, G. W. & Howard, J. C. Transplann Proc. 17, 1844–1846 (1985). 38. Heusser, C., Boseman, M., Nordin, J. H. & Isliker, H. J. Immun. 110, 820–828 (1973).