Silver staining was used to demonstrate nucleoli and nucleolar organizer regions (NORs) in cytopreparations from breast fine needle aspiration (FNA) biopsies, with the resulting black dots being a combination of silver-binding nucleoli and dispersed NORs. Discrete black dots in 200 nuclei were manually counted in 25 silver-stained biopsies; the cytologic diagnoses were made on routine Papanicolaou-stained cytopreparations from the same aspirates. Although malignant breast lesions showed higher counts than did benign breast disease, an overlap of one malignant and three benign lesions occurred. Therefore, the method cannot be recommended for reliably discriminating between malignant and benign routine breast specimens obtained by FNA; it may have some value in assessing tumor behavior.