A single strand conformation polymorphism analysis on polymerase chain reaction (PCR)-amplified genomic DNA was used for the detection of DNA mutations in acid formalin-fixed, paraffin-embedded tissues. Fifty non-small cell lung cancers were screened for mutations in the exon 5 of the p53 tumor suppressor gene. Structural abnormalities of the gene were found in nine (18%) of the tumors examined. The results show that paraffin-embedded tissues fixed in unbuffered formalin can be a good source of DNA for a mobility shift analysis by neutral polyacrylamide gel electrophoresis. The described procedure allows retrospective genetic studies on paraffin blocks available in all pathology departments.