A modified differential display method called RNA fingerprinting was used to identify mRNAs that were differentially expressed during human mesothelial cancer progression. We report the isolation of five different clones. Two clones were expressed in the metastatic mesothelioma cell line M1A and the malignant mesothelioma cell line M1, one clone was expressed uniquely in the metastatic cell line M1A and one clone was solely expressed in the normal mesothelial cells. The other clone was downregulated in the metastatic cell line M1A. The different expression patterns were confirmed by Northern blot analysis. Three clones had no homology to known genes, whereas the other two clones had a striking sequence homology to the M130 antigen and rab 12 mRNA, respectively. The clone that contained a high sequence homology to the M130 antigen mRNA was expressed in the mesothelioma cell lines M1 and M1A and not in any further investigated cancer cell line. This sequence tag may be of interest as a specific mesothelioma tumor marker.