The development of animal models in peritoneal dialysis has led to some breakthroughs in the application of this dialysis modality in clinical practice. These breakthroughs are (1) a better understanding of the physiology and pathophysiology of solute transport and ultrafiltration mechanisms, (2) the observation and integration of the long-term structural and functional alterations of the membrane, (3) a better understanding of the biocompatibility issues involved in PD, leading to the clinical introduction of more biocompatible dialysis solutions and finally, (4) the development of colloid osmotic solutions containing polyglucose polymers for application in the long dwells. Intravital miscroscopy provides information in live animals about diverse functional parameters, such as blood flow rate, vessel diameter, permeability to macromolecules, leukocyte-endothelium interaction, capillary recruitment, and lymph vessel kinetics. Also evaluation of different parameters in a living experimental animal, allowing integration of function and structure is possible. A variety of chronic PD models have been developed, mainly to study effects of long-term peritoneal dialysate exposure on peritoneal membrane function and structure. The implementation of different blocking agents of biochemical substances in these models has elucidated many molecular biological mechanisms involved in these processes. The important roles of aquaporins, vascular endothelial growth factor, nitric oxide, advanced glycation end product formation and their receptor (RAGE) upregulation and the integrated roles of all these factors in the fibrotic alterations of the membrane as observed in patients on long-term PD have been investigated. More recently, genetically modified mice have been used as an important tool to investigate the molecular basis of peritoneal changes during dialysis and during acute peritonitis.