In order to avoid the host foreign-body reaction which is probably responsible for the long-term failure of the artificial membrane diffusion chambers currently used for protecting the implanted islet tissue from rejection, we tested the human amniotic membrane as a possible new tool for enclosing transplanted islets of Langerhans. Bag-shaped chambers were made with human amniotic membranes and the diffusion of 125 I-Insulin out and of D-glucose into the chambers was measured. The diffusion patterns of insulin and glucose were shown to be better than those described for the best artificial membranes, the 50% diffusion being reached at min 42 for 125 I-Insulin and at min 11 for D-glucose. Moreover, it was shown that no lymphocytes diffused into the amniotic membrane chambers. These results, together with the already known characteristics of the human amniotic membrane, induce us to propose it as a suitable material for further experimental work in islet tissue transplantation.