DNA extracted from paraffin-embedded tissues of 30 lung carcinomas, 40 gastric carcinomas and 22 hepatocellular carcinomas was tested for the presence of c-Ki-ras codon 12 point mutation by PCR-RFLP technique. The results showed that 20% (6/30) lung carcinomas and 2.5% (1/40) gastric carcinomas had Ki-ras codon 12 point mutation, but non of the 22 hepatocellular carcinomas displayed this point mutation. Among 6 cases of lung carcinomas of mutation, 4 were squamous carcinomas and 2 were adenocarcinomas.