By means of an AgNOR technique, the authors have carried out a retrospective study on proliferative activity in 170 cases of infiltrating ductal breast carcinoma (so-called carcinoma NOS). The follow-up period was 138 months. A statistically significant correlation was found between AgNOR score and outcome of the disease ("vital status"), clinical stage and OS respectively. By means of discriminant analysis a threshold value of AgNOR score was identified (= 9.5) which distinguished two risk groups among the cases under examination. Those cases with an average AgNOR score below the threshold value showed a favourable prognosis. The cases with an AgNOR score greater than 9.5 had an unfavourable outcome. The authors suggest that AgNOR score may be used as a prognostic parameter in breast carcinoma.