Thirty-one primary breast cancer patients were evaluated by radioimmunolymphoscintigraphy (RILS) and ex vivo scintigraphy (EVS) following subcutaneous injection of human monoclonal antibody In-111-LiLo-16.88. Lymph nodes (370) were assessed by EVS, pathology and immunohistochemistry. The positive predictive value (EVS) for antigen positive nodes, metastatic and hyperplastic, was 90% in stages O-IIB, and the sensitivity and specificity for all stages were 60% and 80% respectively. Four EVS positive nodes with follicular hyperplasia contained micrometastases. RILS and EVS correlate well by the Spearman Rank test (R=0.87). These results suggest RILS may be clinically useful and selectively limit the extent of the surgical procedure.