Malignant pleural mesothelioma (MPM) is a tumour that usually presents a short survival time from diagnosis, but in a small number of patients a longer survival time has been observed. We have studied a series of ten long-term and ten short-term survivors with MPM to assess whether the MIB-1 proliferation index and the p27(kip1) expression correlated with survival. Our results show significant difference in MIB-1 and in p27(kip1) expression between the group of short and longer survival patients. It suggests that the difference in tumour growth fractions may express different biological behaviour and therefore indicate important factors in MPM prognosis.