Silver-binding nucleolar organizer regions (Ag-NORs) were quantitatively counted and DNA content was measured via flow cytometry in 31 cases of hepatocellular carcinoma (HCC). The Ag-NORs counts were 2.1 +/- 1.20 in HCC with diploid DNA content which was significantly lower than the amount (7.0 +/- 2.01) obtained in HCC with aneuploid DNA content (P less than 0.05). The Ag-NORs counts in grade I (well differentiated) HCC were 1.8 +/- 0.24, significantly lower than 4.6 +/- 1.78 and 6.9 +/- 2.29 in grade II (moderately differentiated) and grade III (poorly differentiated) HCC, respectively (P less than 0.05). It is considered that Ag-NORs counting might be a useful indicator in predicting the malignant degree of HCC at the optical level.