In this study 125 primary lung tumours have been immunostained with a panel of 5 anti-p53 antibodies (PAb240, PAb421, PAb1801, CM-1 and C19). These antibodies recognise different epitopes over the full extent of the p53 gene. It is generally believed that immunolabelling identifies only mutant p53 proteins due to the short half life of the wild type protein. The aims of this study were to confirm earlier studies of p53 positivity in human lung tumours and to establish whether or not this bore any relationship to survival. Immunostaining was demonstrated within the nuclei of affected cells in 54% of the 125 lung tumours (59% of 78 squamous cell carcinomas, 52% of 42 adenocarcinomas and 20% of five small cell carcinomas). This confirms previous smaller studies of p53 protein expression in human lung tumours. Survival curves have been drawn for all of the cases considered together and for squamous and adenocarcinomas separately. No differences in survival between p53 positive and negative cases were seen for any group of tumours. This indicates that although p53 may be of considerable importance in the initiation of malignancy it is probably of little significance once a tumour has developed.