robust data assessing the value of procalcitonin ( pct ) for monitoring treatment response in abdominal sepsis are rare , so the study of jung and colleagues published in the previous issue of critical care is most welcome . they concluded that a decrease of pct to 0.5  ng / ml lacked sensitivity to predict treatment response and a decrease of at least 80% from its peak failed to accurately predict treatment response . the value of the study is limited by the small number of patients included , the single - center approach and its observational character . nevertheless , it is to date among the best available evidence we have for these critically ill patients . international databases show that one in four cases of severe sepsis or septic shock is caused by intra - abdominal infection . abdominal sepsis is not just a single disease , but comprises a group of different entities . almost 90% of all intra - abdominal infections are so - called secondary peritonitis and require a primarily surgical approach ( 87% of patients had surgical intervention in the study of jung and colleagues ) . secondary peritonitis consists of community acquired and postoperative nosocomial forms , the latter one following a previous surgical intervention ( anastomotic insufficiency following anterior rectum resection ) . tertiary nosocomial peritonitis is a persistent intra - abdominal infection without a surgically treatable focus , but this point is difficult to assess without an uncontributive reoperation proving that the patient indeed has a tertiary peritonitis . primary inadequate and inappropriate antibiotic regimens for both forms of nosocomial peritonitis are associated with substantially worse prognostic outcome for patients with intra - abdominal infections and result in substantial increases in health care costs . the difficulties associated with abdominal sepsis are complicated by uncertainty about surgical control of the source of the sepsis . do we have any reliable parameters that enable us to decide whether to perform a relaparotomy or not ( in the jung and colleagues study about 20 out of 101 patients required a relaparotomy ) ? an analysis of all investigated markers , including pct , failed to detect specific parameters that can be used under these difficult conditions . current guidelines recommend administration of broad - spectrum antimicrobials within 1  hour of the diagnosis of severe sepsis or septic shock . this recommendation is based on the evidence that delaying antimicrobial therapy in patients with sepsis- related hypotension is associated with increased mortality . pct has been evaluated over recent years as to whether it can be used to detect the presence of different types of infection , treatment failure or adverse outcome . the promising initial publications reporting the results of using serial serum pct concentrations to guide duration of antibiotic therapy in patients with community - acquired pneumonia   have only partially been confirmed in critically ill patients . a recent randomized multicenter trial enrolling critically ill patients   with mainly respiratory tract infection showed that duration of antibiotic therapy can be reduced by a mean of 2.7  days without impact on mortality . but unfortunately , pct had no influence on the duration of antibiotic therapy in patients with intra - abdominal infections . smaller randomized studies show that significant pct - guided reduction of antibiotic exposure can safely be accomplished in patients with severe sepsis and septic shock and in surgical patients with sepsis . more recently , it has been suggested that pct may be of value as a prognostic marker . daily measurements of pct in a general icu population in a recent large multicenter randomized study   were associated with increased use of antibiotics and duration of mechanical ventilation . this commentary has been written by an abdominal surgeon and an intensivist , representing the two disciplines most frequently involved in the treatment of an important subgroup of critically ill patients . in this war against the high mortality from abdominal sepsis , surgeons and intensivists are brothers in arms . the study of jung and colleagues indicates that pct is still a valuable weapon in this war - but far from being the magic bullet .