Rat and rabbit are the most common animal models for peritoneal dialysis. Rats are cheap and easy to keep. Rabbits allow dialysis to be performed for longer periods and in a way very similar to that used in human patients. Recent progress in histomorphometry enables accurate comparison of the biocompatibility of different peritoneal dialysis solutions. Preliminary data in the rabbit indicate that peritoneal dialysis is associated with a change in both the number and size of milky spots, which are peritoneal corpuscles involved in peritoneal defence.