Erosive rheumatoid arthritis (RA) is accompanied by synovial tissue hyperplasia associated with the proliferation of transformed-appearing synovial lining cells. In the present study we have analysed the expression of the p53 tumour suppressor gene in the synovial pannus tissue from patients at various stages of the disease. We used a combination of polymerase chain reaction (PCR) and single-strand conformation polymorphism (SSCP) on DNA and reverse transcription, PCR and sequencing on cDNAs from synovial tissues or purified synovial cell populations of 24 RA and three osteoarthritis (OA) patients. We also studied p53 expression by immunohistochemical analysis. Mutations suspected after SSCP were identified by systematic sequencing of the p53 exon 6, especially in the fibroblast-like, adherent synovial cell population, associated with an erosive disease. Some accumulation of the protein was detected in immunohistochemical analysis of the p53 tumour suppressor gene in the patients' synovial tissues. However, no sign of malignancy was seen in these patients after a 2-year survey. These results show some abnormalities in the p53 tumour suppressor gene in RA patients, but do not allow this to be related to characteristic proliferative features of the rheumatoid synovium.