A study was conducted to assess the reproducibility and prognostic significance of the histopathological grading by using the criteria of Bloom and Richardson. 166 breast carcinomas of the invasive ductal type (NOS - not otherwise specified) according to the WHO criteria, selected from the biopsy material of the years 1980 to 1988 were investigated. 85 of the patients presented axillary lymph node metastases in the mastectomy specimens. A satisfactory correlation of histopathological grades assessed by three pathologists was found in 72.3% of all cases. Fifteen cases (9%) were over- and 31 cases (18.7%) were underestimated compared with an expert's grade. A disagreement of two grades occurred in one case only. In comparison of grade 1 and grade 3 tumours as well as of grade 2 and grade 3 tumours significant differences in the overall survival could be found. Irrespective of statistically significant differences between the three grades in actuarial survival, the histopathological grading is of rather low value for the prediction of prognosis of individual patients.