p53 tumour suppressor gene is often found mutated in Burkitt's lymphoma (BL) cell lines and tumours. We analysed 35 BL tumours for the accumulation of p53 protein, and correlated the results with DNA flow cytometric data on the proliferative activity (SPF), and data on the presence or absence of Epstein-Barr virus (EBV) DNA. More than one-third (37 per cent) of the tumours showed accumulation of p53, which was considered to be consistent with mutation of the p53 gene. Tumours that were positive both for EBV DNA and p53 had significantly higher mean SPF than corresponding EBV DNA negative and/or p53 negative tumours. The proportions of tumour cells with accumulation of p53 appeared to correlate with tumour SPF only in EBV DNA positive BLs. However, there was no apparent association between accumulation of p53 and the presence or absence of EBV DNA. These findings are suggestive of multiple pathways in BL tumour progression.