We recently reported cloning of Streptococcus anginosus (S, anginosus) DNA fragments containing the 16S ribosomal gene from DNA samples of surgical specimens of gastric cancers. To investigate the specificity of S, anginosus infection, Southern blot analysis with S, anginosus 16S riboso- Materials and Methods mal DNA probe and PCR analysis with S, anginosus-specific primers were performed in DNA samples prepared from 15 esophageal cancers, 43 gastric cancers, 16 lung cancers, 10 cervical cancers, 14 renal cell carcinomas, 10 colorectal cancers, and 19 bladder cancers. We frequently found S, anginosus DNA sequences in DNA samples from esophageal cancer and gastric cancer tissues, as well as in those from dysplasia of the esophagus of esophageal cancer patients, No S, anginosus DNA bands were detected by Southern blot analysis on DNAs from the noncancerous portions of the esophagus or the stomach. By PCR analysis with 35 cycles, only 7% of the noncancerous portion of the esophagus was shown to contain S, anginosus sequences, No S, anginosus sequences were found in DNAs from cancers in lung, cervix, and kidney, but they were found in 1 of 10 colon cancers.