It has been reported that the presence of Fc receptor blocking antibodies is associated with normal pregnancy and improved cadaver donor renal transplant survival. The demonstration of the development of such antibody activity in the animal model during one or more pregnancies and the effect of these pregnancies on the survival of a subsequent renal allograft form the major aims of the studies presented in this thesis.A microsurgical laboratory was therefore established at Aberdeen University and the rat renal transplant model developed. Fc receptor blocking activity was assessed using the EA inhibition assay.The results indicate that:I Fc receptor blocking activity was not found in the sera of virgin rats.2 Significant levels of these antibodies were only found after two pregnancies and they occurred in 50% of such cases3 Primiparous animals and those multiparous animals which did not develop EA inhibiting activity rejected renal allografts from the paternal strain in the same time as virgin animals.4 Only multiparous rats sharing over 30% EA inhibition failed to reject transplants carrying paternal specificities. Those animals were capable of rejecting grafts from third party donors suggesting that the Fc receptor blocking antibodies were directed towards paternal antigens.It is therefore suggested that Fc receptor blocking activity occurring as a result of pregnancy in the rat renal transplant model may enhance a renal allograft from the paternal strain. These antibodies may therefore represent a form of donor specific immunosuppression.