AbstractRadionuclide lymphography of the internal mammary and axillary lymph nodes performed on 63 patients with suspected carcinoma of the breast showed good correlation with the histological findings. Twenty‐seven of these patients proved to have carcinoma, 14 with lymph node involvement and 13 without. The remaining 36 had benign lesions.Radionuclide lymphography was accurate in 60 of the 63 cases (95%), giving a sensitivity of 13/14(93%) and a specificity of 47/49(96%). Thus, the technique appears to be sufficiently accurate to suggest its use as a routine noninvasive preoperative examination, enabling the surgeon to reach a decision on patient management, type of operation or radiation therapy. Important additional factors influencing this decision are the possibility of crossover in lymphatic drainage from one breast to the other or a possible malignant lesion on the breast that was not biopsied and would thus go undetected had lymphography not been performed.