Inclusion Criteria:  Patients must have a histologic diagnosis of colorectal cancer. If biopsies were performed at an outside facility, the histology must be reviewed and confirmed by the Department of Pathology at the City of Hope Patients must have tumors that produce CEA as documented by either an elevated serum CEA above the institutional limit of normal or by immunohistochemical methods. Positive CEA immunohistochemical staining, for the purposes of this protocol, is graded 0-3 and the percentage of tumor cells positive is estimated. A positive CEA stain is determined if more than 30% of the tumor cells have an intensity of 2+ or greater Patients must have an advanced disease for which no standard or effective treatment is available. Patients who refuse a standard but non-curative treatment is available may also be considered Karnofsky performance status >= 60% and an estimated survival of at least 3 months Patients must be >= 18 years old as phase I data for the antibody is not available for younger patients. The effects of Ac-225-DOTA-M5A on the developing fetus are unknown. For this reason, women of child-bearing potential and men must agree to use adequate contraception (hormonal or barrier method of birth control or abstinence) prior to study entry and for six months following duration of study participation. Should a woman become pregnant or suspect that she is pregnant while participating on the trial, she should inform her treating physician immediately Adequate bone marrow function as evidenced by white blood count (WBC) >= 4000/ul, absolute neutrophil count >= 1500/ul, platelet count >= 125,000/ul are required Adequate renal function as evidenced by a creatinine =< 1.5 mg/dl and/or a calculated creatinine clearance >= 60 cc/min Adequate liver function as evidenced by bilirubin =< 1.5 mg/dl and alanine aminotransferase (ALT) and aspartate aminotransferase (AST) no greater than 2 times the upper limit of normal. Less than 1/3 of the liver must be estimated to be involved with tumor Presence of measurable disease is required for study entry All patients must be seen in consultation by City of Hope Radiation Oncology and City of Hope Medical Oncology prior to entry onto this trial All subjects must have the ability to understand and the willingness to sign a written informed consent Prior radiotherapy, immunotherapy, or chemotherapy must have been completed at least 4 weeks prior to patient entry on this study (6 weeks if treated with mitomycin-c or nitrosoureas) and patients must have recovered from any expected side effects of prior therapy  Exclusion Criteria:  Patients should not have any uncontrolled illness including ongoing or uncontrolled active infection Patients may not be receiving any other investigational agents, or concurrent biological, chemotherapy, or radiation therapy Pregnant women are excluded from this study because Ac225-DOTA-M5A are agents with the potential for teratogenic or abortifacient effects. Because there is an unknown but potential risk for adverse events in nursing infants secondary to treatment of the mother with Ac225-DOTA-M5A, breastfeeding should be discontinued if the mother is treated with Ac225-DOTA-M5A Patients with recurrent or progressive brain or leptomeningeal involvement with cancer. Patients that have had previous therapies for brain metastasis or leptomeningeal disease with demonstrated response or stable disease at least four weeks after therapy will be eligible for the trial Patients who have received previous radiation to > 50% of their bone marrow Subjects, who in the opinion of the investigator, may not be able to comply with the safety monitoring requirements of the study