The role of the Fallopian tube in assisted reproduction remains unclear. The work described in this thesis was undertaken; (1) to study cyclical oestrogen and progesterone receptor changes in the endometrium and Fallopian tube, (2) to determine ultrastructural similarities and differences between endometrial and endosalpingeal epithelia at the different stages of the cycle, (3) to collect tubal fluid and attempt to isolate tubal specific proteins, and (4) to determine the clinical impact of tubal environment in assisted reproduction by conducting a randomised trial comparing tubal and uterine embryo replacements after in vitro fertilization of oocytes. Oestrogen (ER) and progesterone receptors were studied with specific monoclonal antibodies and employing an immunohistochemical technique. The results showed that, in the tube, both the isthmic and ampullary epithelial and stromal ER increased in the follicular phase to a peak at mid cycle, then declined in the late luteal phase whilst the fimbrial end depicted an opposite pattern of staining. Progesterone receptors persisted in all tubal wall layers and endometrial stroma throughout the cycle, but disappeared completely from endometrial gland epithelium in the late luteal phase. The ultrastructural study showed; (1) an increase in ciliated cells along the tube being highest at the fimbria, (2) late follicular phase increase in cytoplasmic fragments and cellular material within the isthmic lumen, but not in the outer tubal segments and (3) similar secretory pattern and surface epithelial changes in the endometrial gland, isthmic and ampullary tubal epithelia. Gel electrophoresis of tubal flushing demonstrated two non-serum bands appearing in the late follicular and luteal phases of the cycle. One hundred and two women were included in the randomised controlled study. Analysis of all treatment cycles (n=227) showed that; (1) the first attempt resulted in a pregnancy rate per embryo transfer (PR/ET) of 29% for tubal and 20% for uterine replacements, and an implantation rate (IR) of 15% and 12% respectively, and (2) women with unexplained infertility benefit most following tubal transfer (PR/ET; tubal 32%, uterine 15% - IR; 14% and 7% respectively). Factors associated with increased PR in the first attempt include previous pregnancies, absent female or male factors, unexplained infertility, and human chorionic gonadotrophin luteal support. Despite an apparently higher PR and IR following tubal transfer, no significant differences were observed in the multiple pregnancy and live birth rates, nor in the implantation rate in cycles resulting in pregnancy. These findings suggest that the embryos' quality is not enhanced following tubal transfer