The metrics used, thus far, to assess bioartificial organ function are shown to be subjective and requiring validation. Therefore, four categories of correlations are proposed based on, respectively, device, in vitro and in vivo evaluations, and clinical function. Examples are presented whereby the correlations among individual indicators are used as a means to expedite the development of immunoisolated cells. Specifically, a case study illustrating the validation of in vitro indicators of in vivo graft function for the bioartificial pancreas (microencapsulated islets) is summarized. This has revealed thresholds with respect to given metrics relating to in vivo device function, the necessity to couple bioartificial organ design with transplant site selection, as well as the lack of objectivity involved in the evaluation and establishment of hypotheses. Specific quantitative indicators illustrate the need for quality-controlled measures, for example, relating to the tolerance of microcapsule diameter and membrane thickness distributions. Qualitative indices representing fibrosis and device properties (e.g., sphericity) are also used to describe the need for in vitro experiments in the development of bioartificial organs. [on SciFinder (R)]