Correspondence to: A. Ortiz, Unidad de Diálisis,

Although peritoneal dialysis (PD) is a safe and ef-fective form of renal replacement therapy, there are complications that limit long-term technique sur-vival. Among them we find peritonitis, especially those caused by aggressive bacteria such as Staphylococ-cus aureus and Pseudomonas aeruginosa, and perito-neal fibrosis. Both disorders are characterized by changes in numbers of cells. During acute peritoni-tis, there are wild changes in peritoneal fluid cell counts, as well as loss of mesothelial cells. Peritoneal fibrosis is characterized by loss of mesothelium and increased numbers of fibroblasts and peritoneal ves-sels. The number of tissue cells is carefully regulated through the balance between cell birth (mitosis) and cell death, with occasional participation of cell mi-gration or cell transdifferentiation (Figure 1) (1–3)