Although peritonitis is a common complication in patients on CAPD, laparotomy is necessary in only a small proportion of instances. In order to determine the most reliable method to identify which patients require laparotomy, 78 episodes of peritonitis were studied over a 27 month period. History, physical examination and routine laboratory parameters were not useful. If multiple enteric organisms were cultured from a patient and abdominal pain persisted, the results of laparotomy always revealed significant abdominal pathologic findings. No patient required laparotomy if multiple enteric organisms were not recovered. These findings suggest that the only reliable parameter in the selection of patients for laparotomy is the presence of multiple enteric organisms in the dialysate. When abdominal pain persists in a patient with multiple enteric organisms, a laparotomy should be performed.