The authors studied the relationships existing between various cytomorphonuclear parameters recorded on 25 primary breast cancers and their estrogen receptor (ER) content. Cell image analyses of Feulgen-stained imprint smears, allowing determination of morphologic, densitometric, as well as textural parameters, were assessed by using the SAMBA 200 system (TITN, France). The ER levels were measured by the conventional dextran-coated charcoal assay. The authors then divided the 25 cancers into three categories: (1) "ER-negative or poorly positive tumors," i.e., those having less than 50 fmol ER/mg protein; (2) "ER-positive tumors," i.e., those containing between 50 and 150 fmol ER/mg protein; and (3) "ER highly positive tumors," i.e., those having more than 150 fmol ER/mg protein. The authors' results show that ER-negative or poorly positive breast cancers possess cells with bigger nuclei and higher DNA content, related to higher proliferation index than ER-rich tumors. Furthermore, the chromatin pattern of cells from ER-negative or poorly positive breast cancers is significantly more condensed than the thinly textured chromatin of ER highly positive tumors. Cell image analysis of Feulgen-stained imprints is proposed as an additional tool for grading malignancy.