Metastases to the liver presents a common clinical problem in the management of patients with colo-rectal cancer, and are responsible for a high degree of morbidity and mortality associated with this malignancy. Unfortunately, attempts at preventing the development of liver metastases in "high risk" patients has so far been unsuccessful. Ongoing studies of adjuvant chemotherapy have not yet illustrated a significant increase in survival in patients receiving such therapy. The purpose of the study is to investigate the value of adjuvant radiotherapy given in the form of colloidal chromic phosphate P-32 suspension administered via portal vein after radical resection of the primary cancer, in preventing the growth of occult metastases in the liver. Twenty one patients (10 patients of treated group with 11 controls) were followed 18 months after operation. There was no significant change in the CBC and liver functions after administration of P-32 labeled colloidal chromic phosphate. The number of patients who showed local metastases at 18 months were 2 in the treated group and 3 in the control group. While liver metastases occurred in one patient at 6 months and in three at 12 months in the control group, there was no development of liver metastases by 12 months in the treated group. At 18 month follow-up CT scan one patient in the treated group showed a single nodule in the liver. In conclusion liver metastasis rate was lower in the patients who received colloidal P-32 chromic phosphate via portal vein after radical resection of the primary cole-rectal cancer