R. Y.Calne Surgeons are transplanting kidneys in ever increasing numbers-more than 10000 renal allografts have now been reported to the Transplant Registry. With related donors 75% of grafted kidneys continued to function after 2 years, compared with 50% when the donors were unrelated. The therapeutic value is obvious, but the management is largely empirical and results have improved little in the past 5 years. The basic sciences related to tissue transplantation have advanced rapidly. New serological and tissue culture techniques and chemical analysis of antigens and anti bodies have produced complicated data that is almost incomprehensible to the non specialist. Mathematical treatment of genetic probabilities and of immunological kinetics are similarly difficult to follow for those not especially trained. There has always been a gulf between the practical clinician whose patients do not behave like inbred rodents and the biologist who likes carefully controlled experiments with easily observed results. Both realize, however, that predictable and safe control of rejection must involve close collaboration and co-operation between the laboratory and the clinic. Unfortwlately, the different nature of the work and the workers has widened the gap between them. The clinicians tend to improve their techniques and patient care, whilst the biologists seek clearer and more precisely deflned experi ments which lead them to use increasingly artiflcial experimental models.