We investigated insulin-like growth factor II (IGF-II) mRNA in three groups of human liver samples including primary liver cancers, benign liver tumors and cirrhosis; indeed these pathological conditions would allow us to distinguish between different steps in liver carcinogenesis. A 40- to 100-fold increase in IGF-II mRNA was shown in 9/40 of the liver cancer samples as compared to normal adult liver. RNA blot analysis using both IGF-II cDNA and oligonucleotide probes showed the reexpression of two fetal (6 and 5 kilobases) IGF-II transcripts in primary liver cancers and in some cirrhotic adjacent tissues; these included all the samples with enhanced IGF-II expression. By contrast the adult (5.3 kilobases) IGF-II transcript was identified in most of the benign liver tumors and liver cirrhosis; in addition, in some of these samples, the 5-kilobase fetal transcript was also detected. The increase of IGF-II mRNA in some liver cancers is consistent with an autocrine mechanism conferring a selective growth advantage to tumorous liver cells. Furthermore, these results indicate a differential expression of IGF-II transcripts in nonmalignant hepatocyte proliferation (benign liver tumors and cirrhosis) as compared to liver cancer. Finally this study suggests that, in liver cirrhosis and in some benign liver tumors, premalignant proliferative states might be identified by the presence of IGF-II fetal transcripts.