The use hollow fiber membranes for cell encapsulation is being developed as an experimental transplantation technology in which a permselective membrane physically isolates grafted cells from directly interacting with host cells or tissue. Although laboratory characterization of commercial ultrafiltration and dialysis membranes using multi-fiber test modules is well established, a simple apparatus for characterizing the transport properties of small individual segments of hollow fiber membrane has not been described. In the current study, we describe an instrument for evaluating the diffusive and convective transport characteristics of individual cell encapsulation membranes at size scales typically used in animal and human clinical studies. The performance capabilities of the instrument are described, as well as methods for determining hydropermeability, diffusive permeability, and solute rejection.