Although the use of asbestos has been banned in most industrialized countries, it is still a major public health concern. Asbestos fibers are mutagenic and carcinogenic for humans, classified as "carcinogen category 1 (T, R45: can cause the cancer)" in the 25th adaptation of the directive 67/548/EEC. In France, asbestos is thought to be responsible each year for many pulmonary diseases: pleural plaque, bronchogenic carcinoma and mesothelioma (malignant tumor of pleura). In order to better understand the transformation process of pleural cells, we compared the gene expression of mesothelium cells (Met-5A) and mesothelioma cells (MSTO-211H) using high-density filter array (588 genes) and microarray (6.969 genes). Results of both technologies were compared and expression levels of several genes were confirmed by quantitative RT-PCR. Data analysis with GemtoolsTM 2.4 software allows us hierarchical classification of genes of known functions by enzyme, function and pathway clusters and leads to characterize both malignant and normal phenotypes. Finally, the comparison between the two cell lines provides new markers of mesothelioma and pleura. They could be useful for diagnostic, prognostic and therapeutic.