DNA index of twenty-three surgically removed, formalin-fixed and paraffin-embedded liver specimens (10 focal nodular hyperplasias--FNH, and 13 hepatocellular carcinomas--HCC) were studied by flow cytometry. Diploid value appeared in 9/10 FNH (one was hypodiploid), while 10/13 HCC (77%) had DNA aneuploidy (one hypo- and 9 hyperdiploid). The presence of normal DNA content in 3 HCCs suggests that DNA aneuploidy only cannot indicate the malignant transformation of a benign lesion (e.g. FNH).