Chronic renal failure (CRF) remains a major cause of morbidity and mortality world-wide and consumes substantial percentage of health budgets in the developed countries. Dialysis, in particular, continuous ambulatory peritoneal dialysis (CAPD), as a form of therapy in the management of CRF, has its own side effects and can contribute to the morbidity and mortality. The end result of these side effects is loss of effective surface area consequent on the development of peritoneal sclerosis. Peritoneal sclerosis in CAPD occurs gradually over repeated number of dialysis sessions. Serial observations of changes in the peritoneum, as a dialyzing surface, are difficult and it is only available by peritoneal biopsy, which is an invasive procedure. However, the discovery of some markers in the effluents of CAPD patients as a measure of peritoneal membrane status has reduced the need for this invasive procedure. In particular, the discovery of cancer antigen 125 (CA 125) in the effluent has provided a much-needed tool to follow the changes in peritoneal membrane of CAPD patients and prevent the occurrence of much dreaded peritoneal sclerosis.