OBJECTIVE To examine 13 cases of mesothelioma with metastases and compare these with 29 biopsy samples of patients without metastases. Metastatic disease was defined as tumour in which tumour appeared in a different cavity/tissue of the body and which showed no direct spread. Consequently, mediastinal nodal and parenchymal lung spread was excluded. RESULTS Standard sections were prepared and stained according to the manufacturers' protocols. The antibodies used were MIB-1, nm23, Bcl-2, MMP-9, EMMPRIN (CD147) and alpha-catenin. Scoring employed a grading system (0/1/2/3), and was performed by two pathologists independently. The tissues revealed no significant staining differences for MIB-1, Bcl-2, MMP-9 or EMMPRIN, and therefore no linkage to metastatic potential was determined. Alpha-Catenin showed a diminished level of expression in cases of metastatic mesothelioma (P = 0.024), possibly reflecting dimished catenin-cadherin binding and paralleling data from other tumours. nm23 showed greater staining in metastatic tumours when compared with the controls (P = 0.001). Intriguingly, the nm23 staining pattern was the reverse of that expected. This reversed pattern has been noted before in other tumours and therefore a biological prognostic event may exist for this antibody test and mesothelioma metastasis. CONCLUSIONS There may be a place for nm23 and possibly alpha-catenin in immunohistochemical assessment of mesothelioma metastatic potential. However, MIB-1, Bcl-2, MMP-9 and EMMPRIN (CD147) do not show significant staining results.