1. For patients who are potentially curable of cancer of the breast, colon or ovary, radiotherapy can be an effective adjuvant to surgery. The accomplishments of such treatment include: control of regional tumor spread; reduction of metastases incident to manipulation; conversion of a few patients from being inoperable to being operable. Data documenting the contributions of modern radiotherapy are scarce. 2. For patients who, by current knowledge, are not curable of cancer of the breast, colon or ovary, radiotherapy can be an effective palliative agent. Good usage requires specific indications and contraindications, modern techniques, minimization of treatment-produced morbidity, cost and inconvenience.