From 923 breast cancers sent in for hormone receptor determination, 745 diagnostically utilizable Pappenheim-stained biopsy smears at 500-fold magnification were classified into eight atypia groups (1-4 without nucleoli, 5-8 with nucleoli) visually in terms of the severity of the cellular malignancy criteria. The hormone receptor status was determined with the dextran-coated charcoal method. Values from 10 fmol/mg estrogen receptor (ER) and (or) progesterone receptor (PR) content were designated as receptor-positive. There was a decrease in the proportion of receptor-positive results with increasing degree of atypia from 97% in group 2 (cases with only small nuclei without nucleoli) to 37% in group 7 (cases with multiple prominent nucleoli). When the average atypia values of subgroups were compared, the highest values were found for the 222 receptor-negative carcinomas. The marginally receptor-positive values were on average between the receptor-negative and the receptor-positive cases with high values. Both the low-ER and the low-PR have more pronounced criteria of malignancy compared to the respective high-receptor reference group.