Pre-clinical biocompatibility testing of peritoneal dialysis (PD) solutions has become an integral part of new solution development. The construction of a pre-clinical screening program for solution biocompatibility should take a hierarchical approach, starting with in vitro cell viability and function assays. The selection of cell types and assay systems for the in vitro studies should be broad enough to permit a balanced interpretation. Whenever possible, animal models are recommended for the next hierarchical level of testing, followed by human ex vivo study designs. Designs of the latter sort provide evidence that a new solution formulation is exerting an altered biological response in vivo; the response is not purely an in vitro artifact or restricted to a given animal species. This article discusses the various approaches available for biocompatibility testing during the pre-clinical phase of solution development, with an emphasis on the advantages and drawbacks of each method.