In this study we examined the efficacy of the measurement of IAP (serum ancl peritoneal washings) during the treatment of colorectal cancers, and determined the possible benefits of using the IAP measurements from both serum and peritoneal washings. One hundred and six patients (peritoneal washings: 58, peritoneal fluid: 67) were investigated. Serum IAP levels were significantly higher in patients who underwent complicated surgical procedures which involved greater time and blood loss compared to those patients who underwent less involved surgical procedures with little loss of blood and time. In peritoneal washings, up to 66. 7% of cases with peritoneal dissemination showed elevated levels of IAP in the peritoneal cavity, while 37% of cases with no dissemination at surgery macroscopically had positive IAP levels (8 mg/g protein). The results suggest the value of IAP in determining the need for combined immunochemotherapy for patients in an immunosuppressive environment.