To clarify the true nature of liver-cell dysplasia (LCD), a flow cytometric study has been performed. The DNA content of hepatocytes from 26 cases of cirrhosis with diffuse areas of LCD was investigated and compared to that of hepatocytes from 21 control patients with non-neoplastic and neoplastic liver conditions. Flow cytometric analysis was performed on propidium-stained nuclei from archival paraffin-embedded material. Analysis was directed to assessment of diploid as well as non-diploid peaks by calculation of DNA index (DI), using normal hepatocytes present in each sample as individual and specific references. Since only samples containing at least 10,000 nuclei were considered suitable for analysis, 4 of the 26 LCD cases were discarded. Eight of 22 LCD cases had an abnormal DNA content compared with 0/11 non-neoplastic cases (p less than 0.05) and 8/10 hepatocellular carcinomas (p less than 0.05). Non-neoplastic control cases displayed uniformly diploid stemlines whereas hepatocellular carcinomas had in 8/10 cases bimodal or trimodal populations. Thus, LCD is a heterogeneous lesion in terms of ploidy, and the abnormal DNA content observed in some cases supports its pre-neoplastic nature.