PURPOSE: Rectal stump washout has been recommended to prevent implantation of exfoliated malignant cells in the anastomosis after anterior resection for rectal cancer. The aim of this study was to investigate its efficacy, particularly the extent to which the volume of irrigation fluid might influence the efficacy of tumor cell elimination and whether tumor characteristics might influence the result. METHODS: The study comprised 30 consecutive patients operated on by anterior resection for rectal cancer. After cross clamping the rectum below the tumor, a washout sample was collected for examination after every incremental 500 ml of saline irrigation up to 2 liters. The presence of shed cancer cells was correlated with the washout volume and tumor characteristics. RESULTS: Cancer cells were found in 29 of 30 patients (97 percent) in the first sample of irrigation fluid and decreased gradually in frequency and number with increasing irrigation volumes. No cancer cells were demonstrated after 1.5 liters of irrigation in patients with tumor below the peritoneal reflection, whereas cancer cells were still present in one fourth of the patients with tumor located above the peritoneal reflection. Finally, only a small number of cancer cells was confirmed in one patient after 2 liters of irrigation. CONCLUSIONS: The irrigation volume determined the efficacy of rectal washout. With our method, 1 1/2 liters of saline irrigation appears to clear contents from cancer cells in patients with tumors below the peritoneal reflection whereas at least 2 liters is recommended for patients with tumor above the peritoneal reflection. PURPOSE: Rectal stump washout has been recommended to prevent implantation of exfoliated malignant cells in the anastomosis after anterior resection for rectal cancer. The aim of this study was to investigate its efficacy, particularly the extent to which the volume of irrigation fluid might influence the efficacy of tumor cell elimination and whether tumor characteristics might influence the result. METHODS: The study was 30 consecutive patients operated on by anterior resection for rectal cancer. After cross clamping the rectum below the tumor, a washout sample was collected for examination after every incremental 500 ml of saline irrigation up to 2 liters. The presence of shed cancer cells was correlated with the washout volume and tumor characteristics. RESULTS: Cancer cells were found in 29 of 30 patients (97 percent) in the first sample of irrigation fluid in frequency and number with increasing irrigation volumes. No cancer cells were demonstrated a fter 1.5 liters of irrigation in patients with tumor below the peritoneal reflection, whereas cancer cells were still present in one fourth of the patients with tumor located above the peritoneal reflection. Finally, only a small number of cancer cells was confirmed in one patient after 2 liters of irrigation. CONCLUSIONS: The irrigation volume determined the efficacy of rectal washout. With our method, 1 1/2 liters of saline irrigation appears to clear contents from cancer cells in patients with tumors below the peritoneal reflection of at least 2 liters is recommended for patients with tumor above the peritoneal reflection